Used the updated attribute in the GUI

This way, I found a bug in the tests and corrected those and the false code
they produced. The problem was, that I forgot to test that the dirty rects
should be created by using rect.copy(). Otherwise the dirty rects will change,
once the sprites get updated.
The implementation of copy_perm is less messy.
Moved the tests for the helpers to test_helpers.py

This way they will also be found by py.test or nosetests. No need to run
"py.test tests/helpers.py" anymore.
Adding decorators that add trajectories to sprites

Starting with a Delegator class which makes delegating calls to the components
easier. This concept makes use of multiple inheritance: A SpriteDecorator could
be both, a Sprite and a Delegator.
Here are the actual SpriteDecorators

There are four of them:
WithOneAbsTrajectory
WithTwoAbsTrajectories
WithOneRelTrajectory
WithTwoRelTrajectories
Added an example on how to use this software

More example are to follow!
Added a comment to the example
Added a script and brought it to work

gosm (the script) can be used, but has an inconvenient bug:
If you want to run somefile.py with gosm you need to be in the directory where somefile.py is located. Running "gosm path/to/somefile.py" will fail.
Changed sprites_in_module to sprites_in_file

This should fix the bug I spotted when running the example sprite_circle.py
Yup, bug is fixed!

After adapting my script to the changes I made in sprite_collectors everything
worked out fine.
Added example for horizotal & vertical movement