swift234

Parse assignments as part of expr-sequence.

Parse '=' as a binary operator with fixed precedence, parsing it into a temporary UnsequencedAssignExpr that gets matched to operands and turned into an AssignExpr during sequence expr folding. This makes '=' behave like library-defined assignment-like binary operators.

This temporarily puts '=' at the wrong precedence relative to 'as' and 'is', until 'as' and 'is' can be integrated into sequence parsing as well.

Swift SVN r5508