Compile MSVC2010. ERROR is defined in wingdi.h.

Small additional benefit is that this should also speed up
preprocessing, as including QtCore was a bit too greedy...

For future reference: An alternative fix is to define NOGDI before
including windows.h.

Change-Id: I282d4f26624dc38abf3f98b847ccebea5983d331
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>