CSS tweak
add negative regex match-type for ingo sieve rules

-Sieve regex rules are based on Posix which has no support for enhanced
(Perl/Java) features such as lookarounds
-negating a complex regexp as would be made possible by this patch is
simpler than jumping through hoops by use of multiple rules
-Ingo appears to support the 'not regex' case for other backends

Request #12671

Signed-off-by: Michael M Slusarz <slusarz@horde.org>
Looks like maildrop driver already has built-in support for not regex
[mms] Add support for a negative regex test to the Sieve driver (Request #12671; Pete Beardmore <pete.beardmore@msn.com>).
[mms] Add support for a negative regex test to the Maildrop driver.
Simplify test - since it is essentially identical to the existing regex code

Request #12671