Add temp_dir_ttl configuration option to control expiry time in

  program/lib/Roundcube/rcube.php : gc_temp().

Default is 48 hours. Define hard wired minimum of 6 hours.
Fix newmail_notifier issue where favicon wasn't changed back to default (#1489313)

Conflicts:

	CHANGELOG
Merge pull request #111 from dpc22/temp_dir_ttl

Add temp_dir_ttl configuration option
Update changelog