glhelpers: fix glprofile.cpp compilation on VS2012
glhelpers: fix glprofile.cpp compilation on VS2012

std::string was forward declarated only, so I have
include <string>

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