scripts/mkini-win32.bat: use ',' as substitution delimiter; also fix regexp.

Using '!' as the delimiter has an unfortunate clash with cmd.exe's
delayed expansion feature. When delayed expansion is enabled, the
substitution would fail with a syntax error because cmd.exe had
mangled the substitution string before passing it to Perl.

This commit also fixes the regular expression to match the one
found in mkini.sh.