Issue 1104 intersections

These are my current changes for [Issue 1104](http://code.google.com/p/libgdx/issues/detail?id=1104).
There is room for more additional #intersect, #overlap and #contains methods but first I'd like to know if we're in agreement about the interpretation of these methods.

Please review these changes and comment on the 'test cases' in Intersector:1010