Refactor tr/// parsing to work on EBCDIC, fix other bug

Refactor tr/// parsing to work on EBCDIC, fix other bug

This expands the concept introduced for regular expressions in v5.22 of
a portable range, to the transliteration operators.  A portable range
has at least one endpoint expressed as \N{} that indicates that the
Unicode definition is desired, or has the endpoints expressed as both
uppercase ASCII alphabetic letters or both lowercase ASCII alphabetics.

The refactor fixes several EBCDIC problems, and it fixes the problem in
all platforms wherein the first endpoint of a range was not checked to
be <= the final endpoint in UTF-8 strings.

There remains a bug in which if any transliterated code point is larger
than IV_MAX, perl loops.