#2010 - Revise item::find_by_path to search for jpg-converted items.
- added extra $var_subdir argument to item::find_by_path.
- changed item::find_by_path to use $var_subdir to detect if we should look for a jpg-converted item or not (e.g. movie thumbs)
- moved the album thumb detection to item::find_by_path to ensure it knows to look for an exact album match.
- added more sanity checks to item::find_by_path (now has fewer false positive possibilities).

- updated file_proxy to remove the need to guess different movie files.
- updated File_Proxy_Controller - new sanity checks catch previously undetected bug.
- added additional unit tests for item::find_by_path.