[lworld] RFR(M): Multiple compiler fixes and refactoring

[Roland Westrelin]

Hi Tobias,

> http://cr.openjdk.java.net/~thartmann/valhalla/lworld/field_access_fix/

callGenerator.cpp line 921. Shouldn't we know statically if arg is null
(a null litteral) because we filter nulls early? Same question for
parse1.cpp line 617.

Roland.