Make precompiled dalvik opt-in instead of opt-out

the address alignment issues that break skia in SkCanvas::drawRectCoords are a dealbreaker.

Set FORCE_PRECOMPILED_DALVIK to *anything* to play with the files, or to include them so that you can investigate and fix the issue.

Change-Id: Id07adc9b4c741a7916cab3705c92c9daaeca4e10