Update git to v1.7.7.7

This release changes the archive interface so that we now need to pass
argv into write_archive().

Signed-off-by: John Keeping <john@keeping.me.uk>

cgit.h

@@ -11,6 +11,7 @@
 #include <tag.h>
 #include <diff.h>
 #include <diffcore.h>
+#include <argv-array.h>
 #include <refs.h>
 #include <revision.h>
 #include <log-tree.h>
@@ -274,6 +275,8 @@ struct cgit_context {
 	struct cgit_page page;
 };
 
+typedef int (*write_archive_fn_t)(const char *, const char *);
+
 struct cgit_snapshot_format {
 	const char *suffix;
 	const char *mimetype;