Filenames with spaces; output beside the input file; warning fixes (from dev c08eb1bbfa4c)

- Filenames may contain spaces: quote on the command line; filename
  lists use a standalone "/" separator; unseparated names that do not
  exist are rejoined into names that do (announced); leading ~ expands.
- Without -o, output is written to the input file's directory; -o fully
  specifies the output directory and basename.
- "Word not parsed" warnings now appear without -v, only for text that
  survives removal, with correct line numbers.
- New tst/filename_test.sh regression suite.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

mac/machine.cpp

@@ -249,6 +249,7 @@ void Machine::process_katoms(
     if (read) expand_read_katoms(
         katoms, source,
         nonascii, literal, ignore, whitespace, klammers, eval, cond, read);
+    warn_unparsed_katoms(katoms, m_warn_unparsed);
 //    return katoms;
 }