solve the build break due to the lack of this method.

It also propose a solution to the API changes in RegisterContext.

I upgraded also the the python version in the makefile. My linux
installation has python2.7 and AFAIK also the latest ubuntu
has this version of python so maybe is worth upgrading.

Patch by Marco Minutoli <mminutoli@gmail.com>

[Note: I had to hand merge in the diffs since patch thinks it is a corrupt patch.]

llvm-svn: 131313