Added cos_get/put_curr_thd functions in kernel. They save and retrieve
information from the cos_cpu_local_info structure on kernel
stack. They replaced the core_get/put_* functions, which use per_cpu
variables (which also means one more TLB access).
Removed some unused functions/variables (and deleted ipc.S).
Tried to implement per-core freelist for stacks but didn't
finish. Need to move on to the benchmark for the PPOS paper next.

An issue regarding the per-core freelist: when we have multiple
freelists declared in the cos_comp_info structure, the system fails in
llbooter. Going to figure it out when coming back to this.
Merge branch 'ppos' of https://github.com/gparmer/Composite
Merge pull request #83 from interwq/master

PPOS update