interhg: allow more flexible pattern specification (fixes 2/3 of issue699) - something else than "pat" followed by a number can be used as key - something else than "/" can be used as delimiter - "ilmsux" flags (e.g. "i" for case insensitive) can be used

adding a
diff -r 107ba6f817b5 -r 310ce7989cdc a
--- a/a	Thu Jan 01 00:00:01 1970 +0000
+++ b/a	Thu Jan 01 00:00:02 1970 +0000
@@ -1,2 +1,3 @@ confuse str.splitlines
 confuse str.splitlines
 embedded
newline
+clean diff