[build] Warn if libgpm is missing and other minor changes.

* On some misconfigured systems, libgpm is required along with ncurses.
  I haven't been able to figure out the correct way to figure out these
  dependencies without resorting to using external tools like 'nm'. So
  for the moment, if libgpm is not found, at least warn the user that
  the build might fail later.

* Ncurses on OS X does not require libgpm, so there is no need to test
  for it.

* There seems to be an 'AC_DEFINE' _BSD_SOURCE which does not seem to be
   used anywhere. Removing this for now.

* Remove some artifacts left behind by Emacs.

configure.ac

@@ -30,11 +30,11 @@ dnl abssrcdir is the absolute path to the source base (regardless of where
 dnl you are building it)
 case x$srcdir in
 x/*)
-	abssrcdir=$srcdir
-	;;
+    abssrcdir=$srcdir
+    ;;
 *)
-	abssrcdir=`pwd`/$srcdir
-	;;
+    abssrcdir=`pwd`/$srcdir
+    ;;
 esac
 AC_SUBST(abssrcdir)
 
@@ -51,11 +51,11 @@ AC_ARG_ENABLE([profiling],
 
 AC_MSG_CHECKING(gprof(4) profiling support)
 if test x"${enable_profiling}" = x"yes" ; then
-	CFLAGS="$CFLAGS -pg -gstabs"
-	CXXFLAGS="$CXXFLAGS -pg -gstabs"
-	LDFLAGS="$LDFLAGS -pg"
+    CFLAGS="$CFLAGS -pg -gstabs"
+    CXXFLAGS="$CXXFLAGS -pg -gstabs"
+    LDFLAGS="$LDFLAGS -pg"
 else
-	enable_profiling=no
+    enable_profiling=no
 fi
 AC_MSG_RESULT($enable_profiling)
 
@@ -105,7 +105,21 @@ AS_IF([test "x${enable_tinfo}" != "xno"],
     AC_MSG_NOTICE([Building with tinfo linking disabled])
 )
 
-AC_SEARCH_LIBS(Gpm_Open, gpm)
+dnl libgpm is required on some systems where there is a misconfigured ncurses
+dnl and gpm libraries with interdependencies. This check is not required on OS X.
+AS_CASE(["$host_os"],
+    [darwin*],
+    [],
+    AC_SEARCH_LIBS(Gpm_Open, gpm,
+       [],
+       [dnl
+        AC_MSG_WARN(m4_join([ ],
+                    [libgpm not found. If build fails later],
+                    [consider installing gpm dev package])dnl
+        )
+       ]
+    )
+)
 
 AC_CHECK_HEADERS(execinfo.h pty.h util.h zlib.h bzlib.h libutil.h sys/ttydefaults.h)
 
@@ -124,13 +138,6 @@ AX_PATH_LIB_READLINE
 
 LNAV_WITH_SQLITE3("3.0.0")
 
-case "$host_os" in
-    *)
-	# AC_DEFINE([_XOPEN_SOURCE], [500], [Need pread])
-	AC_DEFINE([_BSD_SOURCE], [1], [Need pread])
-	;;
-esac
-
 ALL_LDFLAGS="$LDFLAGS $SQLITE3_LDFLAGS"
 
 static_lib_list="libncurses.a libreadline.a libsqlite3.a libz.a libtinfo.a"
@@ -157,16 +164,16 @@ if test x"${enable_static}" != x"no"; then
     rm -f src/static-libs/*.a
     for libflag in $ALL_LDFLAGS; do
         case $libflag in
-	    -Lstatic-libs)
-		;;
-	    -L*)
+        -Lstatic-libs)
+        ;;
+        -L*)
                 libdir=`echo $libflag | sed -e 's/-L//'`
                 for slib in $static_lib_list; do
                     if test -e "$libdir/$slib"; then
                         ln -sf "$libdir/$slib" src/static-libs/.
                     fi
                 done
-		;;
+        ;;
         esac
     done
 fi