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>

sks/image/image_grid.py

@@ -22,7 +22,7 @@ class Kargs:
         self.number = K.cell_number
         self.hpos = "none"
         self.K_target = target
-        self.K_input_filenames = K.K_input_filenames
+        self.K_input_dir = K.K_input_dir
         self.K_output_dir = K.K_output_dir
         self.K_output_basename = K.K_output_basename
         self.Image_output_dir = K.Image_output_dir
@@ -57,7 +57,7 @@ class Image_grid(klammer_base.Klammer_base):
             self.basenames.append([e[0] for e in self.images[-1]])
             self.captions.append([e[1] for e in self.images[-1]])
         self.cache = image_cache.Image_cache(
-            os.path.dirname(os.path.abspath(self.K_input_filenames)),
+            self.K_input_dir,
             self.Image_search_path,
             verbose=False)