git: update to 1.8.4

No code changes required, just bump the submodule and makefile versions.

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

Makefile

@@ -14,7 +14,7 @@ htmldir = $(docdir)
 pdfdir = $(docdir)
 mandir = $(prefix)/share/man
 SHA1_HEADER = <openssl/sha.h>
-GIT_VER = 1.8.3
+GIT_VER = 1.8.4
 GIT_URL = https://git-core.googlecode.com/files/git-$(GIT_VER).tar.gz
 INSTALL = install
 COPYTREE = cp -r