Selected table row is wrong after changing sort

[rohrlich]

Sorting on a different column should keep the "logically" selected row

[rcoreilly]

added code to maintain selections after updates -- also in base giv code for new / delete -- but current impl is not updating widgets even though sel is correct.

[rcoreilly]

above fixed; note: to do the original request: cache underlying rows of table (not index view rows) and then re-establish those -- requires looking up each row in index view -- a bit expensive.