Add manifest API to request a large heap.

You can now do android:largeHeap="true" on an application.

Doesn't yet do anything, waiting for Dalvik API.

Also tweak package parsing so that the SDK API level is set in the
configuration, allowing manifest resource value selection based on
that.

Change-Id: I6e035f9702a97b055416743b88f83a22ba4a9584