git-gui: fix file name handling with non-empty prefix
-rwxr-xr-x 1813 GIT-VERSION-GEN
-rw-r--r-- 11664 Makefile
-rwxr-xr-x 1372 git-gui--askpass
-rwxr-xr-x 99395 git-gui.sh
drwxr-xr-x - lib
drwxr-xr-x - macosx
drwxr-xr-x - po
drwxr-xr-x - windows