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 bar
adding foo
% state dump
a   0         -1 baz
n 644          0 foo
r   0          0 bar
% status
A baz
R bar
C foo
% state dump
n 666         -1 bar
n 666         -1 foo
% status
! bar
? baz
C foo