git: update to 1.9.1

Everything works just bumping the version in Makefile and commit hash
in submodule. No code changes required.

Makefile

@@ -14,7 +14,7 @@ htmldir = $(docdir)
 pdfdir = $(docdir)
 mandir = $(prefix)/share/man
 SHA1_HEADER = <openssl/sha.h>
-GIT_VER = 1.9.0
+GIT_VER = 1.9.1
 GIT_URL = https://git-core.googlecode.com/files/git-$(GIT_VER).tar.gz
 INSTALL = install
 COPYTREE = cp -r