#1 patch to resolve invalid operation bug in readback test

[Martin]

According to the spec you allways have to use a
fragment program when using float surfaces.
In the readback test a glReadPixels and a glDrawPixels
was issued without using a fragment program.
On my nvidia FX5700LE with driver 76.44 beta on
windows 2000 this resulted in an Invalid Operation error
on every readback float test.
This patch resolves this issue by adding a simple
passthrough fragment program if float surfaces are used
in the readback test.
This patch is against cvs version of gpubench of 21 april
2005.

[Martin]

patch to resolve Invalid Operation bug in Readback test