Improve message when file changes on disk to include moving or renaming

[eppixx]

Case:

1. open a text file
2. change file name
3. Code informs the file has been deleted

Improvement suggestion:

• change the message to "file has been deleted, moved or renamed"
  or
• notice the file has been renamed and ask if code should open the renamed file

[cassidyjames]

The first suggestion sounds easy enough to implement. The latter sounds more ideal but more involved. 😄 I'll get a PR together for the first though!

[ryonakano]

notice the file has been renamed and ask if code should open the renamed file

This might be possible using GLib.File.monitor() with the GLib.FileMonitorFlags.WATCH_MOVES flag and connecting to the GLib.FileMonitor.changed signal.

But I don't think this is necessary and thus I think we can close this issue as fixed in #1505.

[jeremypw]

Probably best to split this into two issues as the original description is vague. The first part is fixed and the second is still open and potentially fixable.

[jeremypw]

Reduced scope of this issue. New issue created about re-opening a renamed or moved document. Closing this issue as fixed by #1505.