/x in patterns now includes all \p{PatWS}

/x in patterns now includes all \p{PatWS}

This brings Perl regular expressions more into conformance with Unicode.
/x now accepts 5 additional characters as white space.  Use of these
characters as literals under /x has been deprecated since 5.18, so now
we are free to change what they mean.

This commit eliminates the static function that processes the old
whitespace definition (and a generated macro that was used only for
this), using the already existing one for the new definition.  It
refactors slightly the static function that skips comments to mesh
better with the needs of its callers, and calls it in one place where
before the code was essentially duplicated.

p5p discussion starting in
http://nntp.perl.org/group/perl.perl5.porters/214726 convinced me that
the (?[ ]) comments should be terminated the same way as regular /x
comments, and this was also done in this commit.  No prior notice is
necessary as this is an experimental feature.