Add functions to test.pl for easier EBCDIC testing

Add functions to test.pl for easier EBCDIC testing

This patch adds functions native_to_latin1($) and latin1_to_native($) to
test.pl.  Use of these in test scripts allows for less special case code
(or deciding to blow it off and just skip EBCDIC platforms).  If a
string is all ASCII, one has always been able to just use it and not
worry about EBCDIC.  But non-ASCII, latin1 characters have been a
different matter.  This allows one to wrap those characters in a
function call and get automatic EBCDIC compatibility.

The functions do not handle UTF-8/UTF-EBCDIC conversions.  This is more
complicated, and I was worried that that part was not appropriate for
test.pl which should use the bare minimum of Perl functionality.  These
functions use tr///, beyond what other parts of test.pl use.