The former code allowed stapio to have two concurrent commands sent
toward the runtime at the same time: one from the main loop and
another one from the signal handling thread.  This is suspected to
have caused occasional lockups.  This new code switches to a deferred
signal handling model, where the signal handling thread merely
increments a counter, and the main loop monitors that count.
Unfortunately, this currently involves switching the main loop's
blocking /.ctl read into a nonblocking poll.

* runtime/staprun/mainloop.c (pending_interrupts): New variable.
  (signal_thread): Increment it.
  (stp_main_loop): Check it.

* runtime/staprun/mainloop.c (stp_main_loop): When a read error happens,
  quit instead of retrying (which can end up in an infinite loop).

* modverify.c (verify_module): Print some messages for verbose > 1.

* runtime/staprun/relay.c (reader_thread): Check switch_file thread flags
  inside inner read-write loop. And clear the flags after switching file.

Currently staprun fails at send_relocation_kernel(), this is because
ppc32 doesn't have ".__start" symbol. I think we should use _stext,
just as other arches.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>