git-gui: fix file name handling with non-empty prefix

Commit e3d06ca (git-gui: Detect full path when parsing arguments - 2012-10-02) fixed the handling of absolute paths passed to the browser and blame subcommands by checking whether the file exists without the prefix before prepending the prefix and checking again. Since we have chdir'd to the top level of the working tree before doing this, this does not work if a file with the same name exists in a subdirectory and at the top level (for example Makefile in git.git's t/ directory). Instead of doing this, revert that patch and fix absolute path issue by using "file join" to prepend the prefix to the supplied path. This will correctly handle absolute paths by skipping the prefix in that case. Acked-by: Andrew Wong <andrew.kw.w@gmail.com> Signed-off-by: John Keeping <john@keeping.me.uk> Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>