#1800 Fix for perl lexer module syntax glitch and repetition operator

[Kein-Hong Man]

A couple of tweaks to fix some breakage for Perl.
(a) Fix module ::-syntax breakage when special characters such as 'x' are used
(b) Added ' and " detection as prefix chars for x repetition operator

Attached LexPerl.cxx and test cases for (a) in perl-test-module-syntax-fix.pl. 'x' and 'y' are more likely to get caught in this glitch here. For (b), examples as follows below. Tweaking the x repetition operator is beginning to feel a bit like whack-a-mole, but hopefully this covers most cases without resorting to a major review of the x handling code.

eval { $x = unpack "sI${mod}s", 'x'x16 };
my $osVolName = "\0"x256;

[Neil Hodgson]

Committed as [43bf70].