glretrace: Don't delete shader in dumping state.
glretrace: Don't delete shader in dumping state.

Allow to retrieve shader source.

Fixes #89.

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