#54 patch for feature request 2953377

[Daniel Gan-Levi]

This is implementation of database file reloading when the file is changed on disk.
This is actually done by moving the UI into lock mode when such change is detected. If the database in memory was already changed since the last open, read-only mode is additionally turned on.
Direct save caused file changes on disk are of course ignored.
The patch is based on trunk revision 385.

[Daniel Gan-Levi]