Improve quick codegen for aput-object.

1) don't type check known null.
2) if we know types in verify don't check at runtime.
3) if we're runtime checking then move all the code out-of-line.

Also, don't set up a callee-save frame for check-cast, do an instance-of test
then throw an exception if that fails.
Tidy quick entry point of Ldivmod to Lmod which it is on x86 and mips.
Fix monitor-enter/exit NPE for MIPS.
Fix benign bug in mirror::Class::CannotBeAssignedFromOtherTypes, a byte[]
cannot be assigned to from other types.

Change-Id: I9cb3859ec70cca71ed79331ec8df5bec969d6745