Added timer interrupt interposition.

Also some hack of detectng timer interference in user space.
Timer interposition: right now we jump back to the Linux timer handler
after cos timer handling. Linux will freeze if we don't let its
handler run. We should find a way to get rid of this, possibly by
using tickless kernel, which probably could survive timer hijacking
Added sanity check on memory initialization.
Removed warning of FPU_FXSR.
Parallel benchmark update: added tests with rate-limit.

Also, removed Linux timer in Composite.
Merge branch 'master' of github.com:interwq/Composite
Fixed a bug of not setting the evt_id in the thread structure. This
could cause not switching to the event handler thread.

Added more benchmark code (some of them needs to be removed later):
time stamp counter skew measurement (in kernel).
Disabled irqbalance process in the python script.

Added benchmark for save/restore pt_regs.

Going to change the reg save/restore of IPC path.
Removed inv cnt (for each invocation, not per core) on the invocation
path (in gen_client_stub) as this impacts multicore performance.
Changed ipc calling convention. Not done yet.
IPC works fine with pt_regs now. Gonna change the input/output regs.
Going to change IPC return path.
Changed IPC return path to use pt_regs. Cleaned the path!
Renamed save/restore macros.
Added user_regs_get/set functions in c code. This way we abstract the
calling convention separately.
Finished changing the syscalls in inv.c. Still a few left in ipc.S --
which could be the hard ones. Note this version doesn't have all syscalls working.
Still debugging. That's for today.
Fixed the switch_thread and ainv_wait asm entries. Everything works
fine now!

Still a couple of syscalls not changed to use new convention:
buff_mgmt and idle. Will come back to them later.
Changed the buff_mgmt syscall to use new calling convention. Not
tested yet.
Changed idle syscall to use new calling convention. Tested and worked.

Note that, LINUX_ON_IDLE should not be set when using multiple cores
for Composite, or FPU_ENABLED is set.