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.