entrycompletion: set_property() should call property setters

entrycompletion: set_property() should call property setters

gtk_entry_completion_set_property() was setting many properties by
directly modifying priv values, bypassing notification invocation and
possibly another actions done by gtk_completion_entry_set_xxx ()
functions.  Fix by invoking set_xxx() instead of setting the property
value directly.

The real bug observerd was that setting text-column property using
g_object_set() caused SIGFPE later when entry completion was about to
appear.  gtk_entry_completion_set_text_column () apparently does way
more important things than just setting priv->text_column member.

https://bugzilla.gnome.org/show_bug.cgi?id=673693