Add git-zip-tree

In the Windows world ZIP files are better supported than tar files.
Windows even includes built-in support for ZIP files nowadays.

git-zip-tree is similar to git-tar-tree; it creates ZIP files out of
git trees.  It stores the commit ID (if available) in a ZIP file comment
which can be extracted by unzip.

There's still quite some room for improvement: this initial version
supports no symlinks, calls write() way too often (three times per file)
and there is no unit test.

[jc: with a minor typefix to avoid void* arithmetic]

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <junkio@cox.net>

git.c

@@ -263,6 +263,7 @@ static void handle_internal_command(int argc, const char **argv, char **envp)
 		{ "stripspace", cmd_stripspace },
 		{ "symbolic-ref", cmd_symbolic_ref, RUN_SETUP },
 		{ "tar-tree", cmd_tar_tree, RUN_SETUP },
+		{ "zip-tree", cmd_zip_tree, RUN_SETUP },
 		{ "unpack-objects", cmd_unpack_objects, RUN_SETUP },
 		{ "update-index", cmd_update_index, RUN_SETUP },
 		{ "update-ref", cmd_update_ref, RUN_SETUP },