glretrace: Don't warn about drawable size inference for pbuffers.
glretrace: Don't warn about drawable size inference for pbuffers.

As these typically have size specified in the creation call.

See in trace referred in issue #306.

swq0553/apitrace,joshua5201/apitrace,EoD/apitrace,surround-io/apitrace,tuanthng/apitrace,schulmar/apitrace,apitrace/apitrace,schulmar/apitrace,schulmar/apitrace,schulmar/apitrace,trtt/apitrace,swq0553/apitrace,swq0553/apitrace,surround-io/apitrace,trtt/apitrace,EoD/apitrace,surround-io/apitrace,EoD/apitrace,EoD/apitrace,surround-io/apitrace,trtt/apitrace,joshua5201/apitrace,joshua5201/apitrace,tuanthng/apitrace,joshua5201/apitrace,apitrace/apitrace,tuanthng/apitrace,EoD/apitrace,trtt/apitrace,swq0553/apitrace,swq0553/apitrace,tuanthng/apitrace,tuanthng/apitrace,surround-io/apitrace,trtt/apitrace,schulmar/apitrace,apitrace/apitrace,apitrace/apitrace,joshua5201/apitrace