convert-svnexternals: fix parsing of wrongly transformed SVN revisions

SVN revision numbers from svn:externals property, which are a multiple
of 1024 (2^10), are transformed by SubGit to contain a binary suffix
("k", "m" and "g" have been checked) in .gitsvnextmodules file.
These aren't valid revision numbers in SVN either.

Examples:
  1024 -> 1k
  2048 -> 2k
  1048576 -> 1m
  1049600 -> 1025k
  1073741824 -> 1g

This led to the following error:
    svn_rev = int(parsed_config[section]['revision'])
ValueError: invalid literal for int() with base 10: '1k'

Signed-off-by: Markus Heidelberg <markus.heidelberg@web.de>
Signed-off-by: Elijah Newren <newren@gmail.com>

README.md

@@ -44,40 +44,44 @@ filter-repo requires:
 
 # How do I install it?
 
-git-filter-repo is a single-file python script, which was done to make
-installation for basic use on many systems trivial: just place the
-script into your $PATH.
+`git-filter-repo` is a single-file python script, which was done to make
+installation for basic use on many systems trivial: just place that
+file into your $PATH.
 
 See [INSTALL.md](INSTALL.md) for things beyond basic usage or special
-cases.  The more involved instructions are only needed if you
-
-  * are working with a python3 executable named something other than "python3"
-  * want to install documentation (beyond the builtin docs shown with -h)
-  * want to run some of the [contrib](contrib/filter-repo-demos/) examples
-  * want to create your own python filtering scripts using filter-repo as a
-    module/library
+cases.  The more involved instructions are only needed if one of the
+following apply:
+
+  * you do not find the above comment about trivial installation intuitively
+    obvious
+  * you are working with a python3 executable named something other than
+    "python3"
+  * you want to install documentation (beyond the builtin docs shown with -h)
+  * you want to run some of the [contrib](contrib/filter-repo-demos/) examples
+  * you want to create your own python filtering scripts using filter-repo as
+    a module/library
 
 # How do I use it?
 
-See the [user
-manual](https://htmlpreview.github.io/?https://github.com/newren/git-filter-repo/blob/docs/html/git-filter-repo.html).
+For comprehensive documentation:
+  * see the [user manual](https://htmlpreview.github.io/?https://github.com/newren/git-filter-repo/blob/docs/html/git-filter-repo.html)
+  * alternative formating of the user manual is available on various
+    external sites
+    ([example](https://www.mankier.com/1/git-filter-repo)), for those
+    that don't like the htmlpreview.github.io layout, though it may
+    only be up-to-date as of the latest release
 
 If you prefer learning from examples:
-  * the [simple example](#simple-example-with-comparisons) below may
-    be of interest
-  * the user manual has an extensive [examples
-section](https://htmlpreview.github.io/?https://github.com/newren/git-filter-repo/blob/docs/html/git-filter-repo.html#EXAMPLES)
   * there is a [cheat sheet for converting filter-branch
     commands](Documentation/converting-from-filter-branch.md#cheat-sheet-conversion-of-examples-from-the-filter-branch-manpage),
     which covers every example from the filter-branch manual
   * there is a [cheat sheet for converting BFG Repo Cleaner
     commands](Documentation/converting-from-bfg-repo-cleaner.md#cheat-sheet-conversion-of-examples-from-bfg),
     which covers every example from the BFG website
-
-External sites also have [alternative formats of the user
-manual](https://www.mankier.com/1/git-filter-repo) available, at least
-for the most recent release.  This also may be beneficial if
-htmlpreview.github.io starts hitting load limits.
+  * the [simple example](#simple-example-with-comparisons) below may
+    be of interest
+  * the user manual has an extensive [examples
+section](https://htmlpreview.github.io/?https://github.com/newren/git-filter-repo/blob/docs/html/git-filter-repo.html#EXAMPLES)
 
 # Why filter-repo instead of other alternatives?
 
@@ -304,9 +308,9 @@ But this comes with some nasty caveats and limitations:
 # Design rationale behind filter-repo
 
 None of the existing repository filtering tools did what I wanted;
-they all came up short for my needs.  No tool provided any of the
-first eight traits below I wanted, and all failed to provide at least
-one of the last four traits as well:
+they all came up short for my needs. No tool provided any of the
+first eight traits below I wanted, and no tool provided more than
+two of the last four traits either:
 
   1. [Starting report] Provide user an analysis of their repo to help
      them get started on what to prune or rename, instead of expecting

contrib/filter-repo-demos/convert-svnexternals

@@ -254,6 +254,21 @@ def get_absolute_svn_url(svnext_url, svn_root_url):
 
   return True, svnext_url
 
+def parse_revision_value(value):
+  """
+  Parse the value of key 'revision' from a .gitsvnextmodules file and return it
+  as integer.
+
+  Used to handle non-numeric values like 1k, 2k, 3k etc. added by SubGit
+  instead of 1024, 2048, 3072 etc., likewise 1m, 2m, ..., 1g, ...
+  """
+  suffix = value[-1]
+  if suffix in "kmg":
+    mult = {"k": 1024, "m": 1024**2, "g": 1024**3}
+    return int(value[0:-1]) * mult[suffix]
+  else:
+    return int(value)
+
 def add_submodule_tree_entry(commit, parsed_config, section):
   """
   Add a submodule entry to the tree of a Git commit.
@@ -271,7 +286,7 @@ def add_submodule_tree_entry(commit, parsed_config, section):
 
   # Get SVN revision
   if parsed_config.has_option(section, 'revision'):
-    svn_rev = int(parsed_config[section]['revision'])
+    svn_rev = parse_revision_value(parsed_config[section]['revision'])
   else:
     # TODO: revision has to be guessed according to commit timestamp, skip for now
     return False