handy.h: Solve a failure to compile problem under EBCDIC

handy.h: Solve a failure to compile problem under EBCDIC

handy.h is included in files that don't include perl.h, and hence not
utf8.h.  We can't rely therefore on the ASCII/EBCDIC conversion
macros being available to us.  The best way to cope is to use the native
ctype functions.  Most, but not all, of the macros in this commit
currently resolve to use those native ones, but a future commit will
change that.