submodule: port resolve_relative_url from shell to C

diff --git a/git-difftool.perl b/git-difftool.perl
index 9a1054a2bb9d72d10aeb88c6bdf1d47b0fde1a75..488d14b153e50f69fcfb0c732cc8c23cf4b643de 100755 (executable)
--- a/git-difftool.perl
+++ b/git-difftool.perl
@@ -47,13 +47,9 @@ sub find_worktree
 
 sub print_tool_help
 {
-       my $cmd = 'TOOL_MODE=diff';
-       $cmd .= ' && . "$(git --exec-path)/git-mergetool--lib"';
-       $cmd .= ' && show_tool_help';
-
        # See the comment at the bottom of file_diff() for the reason behind
        # using system() followed by exit() instead of exec().
-       my $rc = system('sh', '-c', $cmd);
+       my $rc = system(qw(git mergetool --tool-help=diff));
        exit($rc | ($rc >> 8));
 }
 
@@ -74,9 +70,7 @@ sub use_wt_file
        my ($repo, $workdir, $file, $sha1) = @_;
        my $null_sha1 = '0' x 40;
 
-       if (! -e "$workdir/$file") {
-               # If the file doesn't exist in the working tree, we cannot
-               # use it.
+       if (-l "$workdir/$file" || ! -e _) {
                return (0, $null_sha1);
        }