Fix #1466 : Performance warning: Send Buffer Watermark
Add external ip alert handler to core
Ensure status message is reset after leaving Error state

Also clean up comments in core.py
Add TorrentStorageMovedEvent for #637
Fix #2006 : Display error when moving storage location fails

Adds handler for storage_moved_failed_alert and then sets the
torrent to Error state and pauses it.
Fixed small bug in path_combo_chooser

The delete-text event was triggered when setting the text in the text entry.
The completion popup was then displayed when it shouldn't. Fixed by blocking
the signal while setting the text.
Flake8'd gtkui/path_combo_chooser