bgo#315462 - Make GtkLabel deal with too-small height allocations gracefully

bgo#315462 - Make GtkLabel deal with too-small height allocations gracefully

Previously we would always align the top of the text with the label's allocation-plus-padding.
However, this makes a single-line label inside a GtkButton look badly clipped when the button
has a smaller allocation than its requisition.  So, for single-line labels we respect the
alignment even if it doesn't fit within the label's allocation.  But for multi-line labels, we
give preference to showing the first line, to give the user some context.

Signed-off-by: Federico Mena Quintero <federico@novell.com>