Only use liberal file pattern matching in the terminal server listfile funcs

Commit 3a3c889b (2 years ago now) changed loadfiles() to use liberal file
matching (e.g. "syncterm.exe" matched both "syncterm.exe" and
"syncterm_v1.2b.exe").

This could produce surprising results when doing file list querieis/operations
with the FileBase methods via JS (e.g. jsexec utils) and (now that I look at
it), the FTP server too.

So we should not have been doing liberal file matching *everywhere* loadfiles
is used, just where it was a usability issue (due to displayed filenames being
truncated to 12 chars for <=80 column terminals).

Now solved by add/use of new liberal_filepattern() function only in the
built-in file listing methods: sbbs_t::listfiles() and sbbs_t::listfileinfo().

Note: Custom JS file searching/listing scripts may now need their own
work-arounds for this usability issue, if they have it.