added imgbox.com images and galleries
non-successful attempt to fix #172: Right mouse button option prevents spell check corrections

Improves debug message.  Changes event target.  But same problem.
Fixed bug where context menu sometimes didn't appear, e.g. when using Shift as described in a comment on #144.
The fix ensures that _postponeContextMenuEvent is always set true after _handleContextMenu().
Fixed #177: Right mouse button option in 3.2beta1 prevents spell check corrections.

The fix is to allow the context menu to pop up immediately on text areas, which allows the
spell checker to show suggestions.  This means if you try to right-drag from a text area onto a
link or image, you'll see a context menu, but that's probably not a common usage.