StrictMode: gather and return violating stacks in Binder replies

Now, when Thread A has a strict mode policy in effect and does a
Binder call to Thread B (most likely in another process), the strict
mode policy is passed along, but with the GATHER penalty bit set which
overrides other policies and instead gathers all offending stack
traces to a threadlocal which are then written back in the Parcel's
reply header.

Change-Id: I7d4497032a0609b37b1a2a15855f5c929ba0584d