Some improvements to the file-name cleaning code:

- Removed the CFN_KEEP_LEADING_DOT_DIR flag for clean_fname().
- Explicitly add an implied dot-dir to the transfer rather than keeping
  a leading a "./" prefix as a part of a relative pathname.
- Added the CFN_KEEP_DOT_DIRS flag for clean_fname().
- Added the SP_KEEP_DOT_DIRS flag for sanitize_path().
- Call clean_fname() a couple more times.