t/re/charset.t: Fix comment, test names

Some of the test names have hard-coded values that are wrong.  This uses
a calculated value.
t/lib/charnames/alias: Add comment
PATCH: [perl #121630]: perlpod clarification
mktables: Add comment
XS-APItest/t/handy.t: Change output message

On EBCDIC platforms, the output is not in terms of \N{U+}; change text
to \x{ }
t/test.pl: Use existing variable instead of recalculating

If the current platform is ascii is available already in a variable.
Use that instead of inventing a different paradigm.
t/run/locale.t: Rmv obsolete complicated idiom

See http://nntp.perl.org/group/perl.perl5.porters/213369
t/run/locale.t: Skip some tests for some shells

Some sh programs don't accept changes of environment variables like
LC_ALL to invalid values.  For these the tests aren't testing what they
think they are, so change them to just return the expected value, so
they will pass.  This effectively skips the tests when run on these
shells.  See http://nntp.perl.org/group/perl.perl5.porters/214503
perlre: Clarify /x eol can't be escaped