Fix a buffer aging problem in new r300 code that could lead to hangs with some apps.
Fix a buffer aging problem in new r300 code that could lead to hangs with some
apps.

Obtained from:	DRM CVS

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase