Merge character class handling revamp topic branch into blead

Merge character class handling revamp topic branch into blead

This sequence of commits cuts down the amount of duplication in handling
character classes (like \w, [:graph:]).  There are three principal
components: 1) refactor a switch statement in regcomp.c to have common
code for most of the possible classes; 2) replace the 30 regops that
handle these classes by just 4 (effectively) distinct ones; 3) deprecate
the functions callable from XS that do character classification.  XS
code should instead (if they weren't already) use macros in handy.h to
accomplish this purpose.