main: Log key points of the main loop.

import2ledger/__main__.py

@@ -25,6 +25,13 @@ class FileImporter:
                 importers.append(importer)
         if not importers:
             raise errors.UserInputFileError("no importers available", in_file.name)
+        else:
+            logger.debug(
+                "%s can be imported by %s",
+                in_path,
+                ", ".join("{}.{}".format(importer.__module__, importer.__name__)
+                          for importer in importers),
+            )
         source_vars = {
             'source_abspath': in_path.absolute().as_posix(),
             'source_absdir': in_path.absolute().parent.as_posix(),
@@ -44,6 +51,7 @@ class FileImporter:
                     if hook_retval is None:
                         pass
                     elif hook_retval is False:
+                        logger.debug("%s import aborted by %s", in_path, type(hook).__name__)
                         break
                     else:
                         entry_data = hook_retval