Several fixes for JIT and self-verification under corner cases.

1) Fix the self-verification mode to handle backward chaining cell
properly when a single-step instruction is in the middle of the cyclic
portion of the trace. Then found issue 2 when changing the JIT
threshold to 1.
2) When the code cache is full, the VM may stop making forward progress
and bounces back and forth between the debug and fast intepreters as the
translation request is constantly rejected. The fix is to stay in the
debug interpreter until the corner case condition is cleared. Then found
issue 3.
3) Under self-verification mode, the code cache reset request may get
delayed indefinitely due to spurious indication that a thread is
running JIT'ed code. Trivial fix - make sure the inJitCodeCache flag is
cleared.

(cherry-picked from dalvik-dev)

Change-Id: Ic0b9952c0ae545f68f7eb2ae06a82a634ab62e9e