Add fixes for testing EBCDIC to blead

This branch contains fixes to test files to pass on both ASCII and
EBCDIC platforms.  Some of these are a couple years old, and have been
lingering in the EBCDIC branch until now.

These changes are all to core code that is not dual-lifed, and that
doesn't have any other complications.  Future commits will deal with
the ones left out of this commit.

Some commits generalize the test to work on any platform, including a
non-EBCDIC one, should there ever be one, unlikely as that may be.  The
subjects of these commits say something like "generalize to non-ASCII
platforms."

Some commits rely on EBCDIC and ASCII properties, and would have to be
revised if Perl were ever to work on a platform with some other
character set.  These typically mention EBCDIC in their subject lines.

Some commits merely skip some tests on EBCDIC platforms.  These were
because of several possible reasons.  One is that the test is specific
to a particular EBCDIC code page, and I did not wish to expend my time
in handling all those.  Another similar one is that there would be a
significant amount of work in converting the test, too much for me to
undertake, and I don't think the value added was worth it.  And some are
just because of the inherent qualities of EBCDIC don't fit.  For example
UTF-EBCDIC doesn't have the capacity to handle very large code points
that can be handled on 64-bit ASCII platforms.  Or the tests are just
for porting when we generate a Perl to ship; which we never will do on
an EBCDIC platform.