pgit.sh: Use plain directory path for diff prefix

The diff source and destination in diff used to be a/path/to/file.txt and
b/path/to/file.txt which differed from cvs diff -u. Changed that, now make diff
in the toplevel directory creates usable patches for all sources.

Signed-off-by: Jan Lindemann <jan@janware.com>

scripts/pgit.sh

@@ -119,7 +119,7 @@ diff()
 	cd $pdir
 	for d in $pdirs; do
 		# marker $d
-		run_git -C $d diff --src-prefix=a/$d/ --dst-prefix=b/$d/ "$@"
+		run_git -C $d diff --src-prefix=$d/ --dst-prefix=$d/ "$@"
 	done
 )}