Issue 940 - Exception generating js for prefixed toplevel fields

Issue 940 - Exception generating js for prefixed toplevel fields 
http://code.google.com/p/dart/issues/detail?id=940

Talked to Gilad about the abiguity of language spec between prefix identifiers and method invocation. P.id(...) looks like o.m(...) to the parser at the moment.
Local fields are correctly represented in the AST as unqualified invocations.

R=zundel,mmendez
BUG=
TEST=

Committed: https://code.google.com/p/dart/source/detail?r=2910

[scheglov, 2011-12-28 21:37:52]

lgtm

[zundel, 2012-01-03 15:02:48]

lgtm