enchant.Map render order bugfix for Issue #296

Adjusted the order of the buffer redraw for the enchant.Map to fix the
1-frame lag Issue #296
Previously, the map would be updated during the execution of the render
event which is dispatched before e.g. the cvsRender is executed. In the
update function the map's offset is compared to the previous offset and
if these offsets do not match the map buffer will be updated
accordingly.
However, the maps offset value will be updated during the cvsRender call
and therefore the update of the buffer will happen during the execution
of the next render event -> 1 frame delay.
Now the buffer update will be executed within the cvsRender or domRender
calls.

Added new test cases and adjusted behaviour of the redraw test case for
the enchant.Map rendering to test for the erroneous behaviour described
in Issue #296