v0.5.1: merged r1088-r1093

PyCAM v0.5.1 release notes (2011/06/13):

This new release of PyCAM contains one important new feature (extrusion of 2D
models) and many small fixes and improvements. Windows users will enjoy a more
modern look of the GUI theme and Linux users will be happy about a packaging
with better integration into the desktop. Additionally the 3D preview
performance improved drastically.

Read the detailed list of changes in the developer blog:
http://fab.senselab.org/node/230