rtglobal: Add rtglobal scheduler to hypervisor

This is the core rtglobal patch. It adds the new rtglobal scheduler to
the hypervisor, as the non-default scheduler. The rtglobal scheduler
supports Earliest Deadline First real time scheduling scheme. This is still in the development phase.
xl for rtglobal scheduler
libxl for rtglobal scheduler
libxc for rtglobal scheduler
Merge branch 'rtxen-v1.3' of https://github.com/pennpanda/xenproject into rtxen-v1.3