Fix RoundedRectangle.contains(x,y) after resizing thanks to Joshua Hertlein

When resizing with setWidth() / setHeight() the points are set to dirty, but
the dirty flag wasn't checked in contains(x, y), reusing old values.

Aside: Added TestNG dependency + couple of unit tests for RoundedRectangle

Original issue: https://bitbucket.org/kevglass/slick/issue/41/roundedrectangles-setwidth-and-setheight