view: set_caret_cursor_position should emit "cursor-moved" if applies

https://bugzilla.gnome.org/show_bug.cgi?id=701746
a11y: fixing implementation for atk_text_set_caret_offset

It uses the recently added ev_view_set_caret_cursor_position

https://bugzilla.gnome.org/show_bug.cgi?id=701746
a11y: cleaning implementation for atk_text_get_caret_offset

If caret access is not enabled (or in any other error) caret_offset
should be -1, and not one based on the gtktextbuffer.

Based on a previous patch by Joanmarie Diggs

https://bugzilla.gnome.org/show_bug.cgi?id=701746