charnames pod: Typo, clarification
charnames: comment, error message clarifications
charnames: Enforce better file name rules

The code says that identifier syntax is required for a file name, but
the code accepted any sequence of \w's.
charnames: :alias alone implies :full

The documentation says this is how it should behave, but only 1 of the
three paths in the code did it, and in fact there was a test to the
contrary.

I'm only adding a test for one of the two fixed paths, as the other one
appears to require a weird file name.
charnames: Deprecate character names with spacing issues

A user-defined character name with trailing or multiple spaces in a row
is likely a typo, and hence likely won't match what the other uses of
it.  These names also won't work if we extend :loose to these.  This
now generates a warning.