swift234

Improve mutability diagnostics for parameters to add a note inserting/changing
a 'var' modifier on the parameter, e.g.:

x.swift:44:5: error: cannot assign to 'let' value 'a'
  a = 1
  ~ ^
x.swift:43:8: note: change 'let' parameter to 'var' to make it mutable
func f(let a : Int) {
       ^~~
       var
x.swift:48:5: error: cannot assign to 'let' value 'b'
  b = 2
  ~ ^
x.swift:47:8: note: mark parameter with 'var' to make it mutable
func g(b : Int) {
       ^
       var

Also fix a bug where we'd incorrectly suggesting adding 'mutating' to a class
method when assigning to self in some cases.



Swift SVN r28926