Revert "STENCIL_VALUE_UNKNOWN for DECR/INCR/INVERT"

This reverts commit 59d3b92e710de1ed89b75401e223b24de2ca40fe.

Revert "zero alpha if stencil op consistently says to zero for format 5551 as well"

This reverts commit ed07a7f4111de8ecd3b6feb4e32597bbd8809c0b.
Merge branch 'master' of http://github.com/hrydgard/ppsspp