Clean up the IO in the examples.

Make the examples consitently use the log/abort_example functions so that the
examples do not seem to "do nothing" on Windows. Additionally, remove the
superfluos code after the abort_example() calls.
Consistently check for the success of al_init() in the examples.
Consistently check for the al_create_display success in the examples.

Also move some code which might crash if the display failed to create.
ex_premulalpha was missing an include for common.c
[python] Made the python wrapper work again.

The C parser couldn't understand enums using values defined later, which the primitives addon uses now. Implemented it by re-evaluating enum expressions a second time.