Momoize the results of isinstalledpkg()
Momoize the results of isinstalledpkg()

PR:		bin/116452
Submitted by:	wollmann
MFC after:	7 days

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