These are analogous to QTableView::resizeColumnToContents(i) and
resizeColumnsToContents().  Double-clicking the header
near a width adjustment boundary still provides a means for the user
to do this if the application doesn't do it programmatically.

Change-Id: Ibded0c9f255301b461dac7080901fc6065fdbe5e
Reviewed-by: Caroline Chao <caroline.chao@digia.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>