Change rune-specific #defines from _CTYPE_ prefix to _RUNETYPE_ prefix

Similar to what NetBSD did around 2010, this lets us move some defines
in ctype.h to the _CTYPE_ prefix. No functional change.

"makes sense" deraadt, ok sthen@ tb@

Simplify wctype() and wctype_l(): we have one set of classification
types used by all (== both) locales; put their implementation in one
file and make the mapping static there. The rl_wctype member of
_RuneLocale and its initialization go away at the same time.

ok schwarze@