Update git to v1.7.5.4

Some changes to diff options:

- no_merges has become the more general max_parents
- path restriction now uses struct pathspec

Signed-off-by: John Keeping <john@keeping.me.uk>
diff --git a/ui-stats.c b/ui-stats.c
index 59f4c1e..51dd6a2 100644
--- a/ui-stats.c
+++ b/ui-stats.c
@@ -239,7 +239,7 @@
 	init_revisions(&rev, NULL);
 	rev.abbrev = DEFAULT_ABBREV;
 	rev.commit_format = CMIT_FMT_DEFAULT;
-	rev.no_merges = 1;
+	rev.max_parents = 1;
 	rev.verbose_header = 1;
 	rev.show_root_diff = 0;
 	setup_revisions(argc, argv, &rev, NULL);