The error message due to lack of the default value for an extra field
was not as informative as it should be.

Fixed with improving the scheme of gathering, propagating and reporting
errors in applying rows events. 
The scheme is in the following.
Any kind of error of processing of a row event incidents are to be 
registered with my_error().
In the end Rows_log_event::do_apply_event() invokes rli->report() with the 
message to display consisting of all the errors.
This mimics `show warnings' displaying.
A simple test checks three errors in processing an event.
Two hunks - a user level error and pushing it into the list - 
have been devoted to already fixed Bug@31702.

Some open issues relating to this artifact listed on BUG@21842 page and
on WL@3679.
Todo: to synchronize the statement in the tests comments on Update and Delete
events may not stop when an extra field does not have a default with wl@3228 spec.