Fixed a test failure that occurs when the specified font is not installed.

On systems where 'Liberation Sans' is not installed out-of-the-box
(e.g. Ubuntu Server, OpenSuse Server) it falls back to 'DejaVu Sans',
which makes the GetHashCode_NameDiffers_HashesNotEqual() test fail as
the two font names are now equal. Instead we use 'Arial' and 'Courier New'
which resolve to different fonts on most systems.

Changes licensed under MIT/X11.