mpick: add 'cc' filter expression

Closes https://github.com/leahneukirchen/mblaze/issues/186

man/mpick.1

@@ -92,7 +92,7 @@ tests are given by the following EBNF:
                       | T )?     -- *1024*1024*1024*1024
              | cur               -- index of cur message
 
-<hdrprop>  ::= from | to | subject | <str>
+<hdrprop>  ::= from | to | cc | subject | <str>
 
 <decodeop> ::= . addr          -- match address parts
              | . disp          -- match address display parts

mpick.c

@@ -601,6 +601,8 @@ parse_strcmp()
 		h = xstrdup("from");
 	else if (token("to"))
 		h = xstrdup("to");
+	else if (token("cc"))
+		h = xstrdup("cc");
 	else if (token("subject"))
 		h = xstrdup("subject");
 	else if (token("path"))