Change GIT-VERSION-GEN to call git commands with "git" not "git-".

GIT-VERSION-GEN can incorrectly return a default version of
"v1.3.GIT" because it tries to execute git commands using the
"git-cmd" format that expects all git commands to be in the $PATH.
Convert these to  "git cmd" format so that a proper answer is
returned even when the git commands have been moved out of the
$PATH and into a $gitexecdir.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

GIT-VERSION-GEN

@@ -5,7 +5,7 @@ DEF_VER=v1.3.GIT
 
 # First try git-describe, then see if there is a version file
 # (included in release tarballs), then default
-if VN=$(git-describe --abbrev=4 HEAD 2>/dev/null); then
+if VN=$(git describe --abbrev=4 HEAD 2>/dev/null); then
 	VN=$(echo "$VN" | sed -e 's/-/./g');
 elif test -f version
 then
@@ -16,7 +16,7 @@ fi
 
 VN=$(expr "$VN" : v*'\(.*\)')
 
-dirty=$(sh -c 'git-diff-index --name-only HEAD' 2>/dev/null) || dirty=
+dirty=$(sh -c 'git diff-index --name-only HEAD' 2>/dev/null) || dirty=
 case "$dirty" in
 '')
 	;;