Char classification: drop __ischareq(), avoid CC warnings..
For one this changeset tweaks (def.h: use 8 bit for char
classification.., 2012-10-01) and (Avoid warnings for the bltin
ctype stuff.., 2012-09-22) in that cntrlchar() simply checks for
the presence of C_CNTRL instead of the exclusive C_CNTRL value.
This makes __ischareq() unnecessary.
Also upperconv() and lowerconv() perform casts to avoid compiler
warnings on possible overflows (or, more exactly, "assuming
signed overflow does not occur")