Extract Git::SVN from git-svn into its own .pm file.

Except for adding the 1; at the end, this is a straight copy & paste.

Tests still pass, but its doubtful Git::SVN will compile on its own
without git-svn being loaded.  Next commit will fix that.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Eric Wong <normalperson@yhbt.net>

perl/Makefile

@@ -29,6 +29,7 @@ instdir_SQ = $(subst ','\'',$(prefix)/lib)
 
 modules += Git
 modules += Git/I18N
+modules += Git/SVN
 modules += Git/SVN/Memoize/YAML
 modules += Git/SVN/Fetcher
 modules += Git/SVN/Editor