- Switch @mutable to be a tri-state attribute that is invertable with @!mutable.
- Move the semantic form of 'mutable' to being a bit on FuncDecl instead of
something in DeclAttrs. The former is a binary bit, the later is a tristate
which differentiates between "not present", "present and set" "present and inverted".
- Diagnose some invalid uses of @mutable, e.g. on class methods.
- Make setters default to mutable, and allow them to be switched with @!mutable.
Swift SVN r11439
Rather than performing a two-pass walk over all of the constraints in
the system to attach them to type variables, use the existing type
variable -> constraints mapping in the constraint graph to make this a
faster single-pass process. Also clarify the type bindings a little
bit. Improves type checking time for the standard library by ~3%.
Swift SVN r11098
