Updated Italian translation
Updated Latvian translation
Updated Latvian translation
UndoManager: bug fix for empty user actions

Empty user actions can happen in gnome-builder for example.
UndoManager: remove #if 0 sections

The code will be moved to a branch.
CompletionContext: more robust code

Buffer changes are now handled correctly.
gtk_source_completion_context_get_iter() returns a gboolean to tell if
the iter was set.

Connecting to the mark-set signal is not needed, because the mark can be
set only in set_iter().