revset: also parse x^: as (x^): Given x^:y is (x^):y, this seems sensible.

revset: resolve ambiguity of x^:y before alias expansion This is purely a parsing problem, which should be resolved before alias expansion.

revset: add test for resolution of infix/suffix ambiguity of x^:y This is the test for 805651777188, and I'm going to fix the failure of 'x^A' where 'revsetalias.A=:y'.