swift234

Implement syntax changes for in-place methods.

Rename 'assignment' attribute of infix operators to 'mutating'. Add
'has_assignment' attribute, which results in an implicit declaration of
the assignment version of the same operator. Parse "func =foo"
declaration and "foo.=bar" expression. Validate some basic properties of
in-place methods.

Not yet implemented: automatic generation of wrapper for =foo() if foo()
is implemented, or vice versa; likewise for operators.

Swift SVN r26508