Return filenames as strings (not pathnames) in compfile and compile_file

Return filenames as strings (not pathnames) in compfile and compile_file

On success, the value returned by compfile and the last element of
the list returned by compile_file have been lisp pathnames instead
of strings.

Returning a pathname instead of a string is not consistent with how
other filenames are returned by compile_file, translate_file, batch,
load, etc.  It's also problematic because pathnames print like strings
by default in Maxima, and one would probably expect these filenames to
be strings, but Maxima doesn't handle them like strings.

In Maxima 5.0 compfile returned a pathname, but older sources show
that it returned a string instead under some older lisp dialects.
Also in Maxima 5.0 compile_file returned a pathname (well it returned
the same value that COMPILE-FILE returned, but CLtL1 doesn't seem to
actually specify the return value).  compile_file was not present in
very old sources (although a completely different compile_lisp_file
was present).