Add extend_pcr
Add extend_pcr

We want to be able to extend PCRs for testing purposes, so add support for
that.

mjg59/python-tss,JohnVillalovos/python-tss-1,mjg59/python-tss,JohnVillalovos/python-tss-1,ph4r05/python-tss,ph4r05/python-tss