regcomp.c: Handle more cases of tricky fold chars

regcomp.c: Handle more cases of tricky fold chars

Certain characters are not placed in EXACTish nodes because of problems
mostly with the optimizer.  However, not all notations that generated
those characters were caught.  This catches all but those in \N{}
constructs; which is coming later.

This does not use FOLDCHAR, which doesn't know the difference between
/d and /u; instead it uses ANYOFV, which does handle those cases already,
at the expense of larger (in storage) regexes for these few characters.
If this were deemed a problem, there would be some work involved in
adding FOLDCHARU, and fixing the code where it doesn't work properly now.