difftool: avoid double slashes in symlink targets

When we add tests for symlinks in "git difftool --dir-diff" it's easier
to check the target path if we don't have to worry about double slashes
separating directories.  Remove the trailing slash (if present) from
$workdir before creating the symlinks in order to avoid this.

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-difftool.perl

@@ -209,7 +209,9 @@ sub setup_dir_diff
 	delete($ENV{GIT_INDEX_FILE});
 
 	# Changes in the working tree need special treatment since they are
-	# not part of the index
+	# not part of the index. Remove any trailing slash from $workdir
+	# before starting to avoid double slashes in symlink targets.
+	$workdir =~ s|/$||;
 	for my $file (@working_tree) {
 		my $dir = dirname($file);
 		unless (-d "$rdir/$dir") {