- introduce PROC_STOPPED flag, which tracks whether the process is
stopped on PROC_STOP in the kernel, rather than implicitly deriving
this from PM_SIG_PENDING;
- make the process resumption test based on current state rather than
state transitions;
- add and clarify several flag checks in the signal handling code;
- add test79 to test signal handling robustness.
Change-Id: Ic8c7527095035b300b56f2ab1b9dd190bd4bf001
