Removed silly error that should never happen

When there is no "map document", the automap action is disabled.

It's not the user's problem when this function is called without
a document, so no point in having an error message.
Display errors non-modal when applying automatic automapping rules

Popping up a message box while painting repeatedly is tremendously
annoying (and seems to break the delivery of the mouse release event).
Show any warnings or errors that happen when automatically applying
automapping rules in the status bar instead.
Fixed map pixel size preview for staggered maps
Merge branch '0.10'