Protocols with generic where clause fail to parse

[justin]

Example

protocol Foo where BarType: Equatable { }

Result

(program [0, 0] - [1, 0]
  (protocol_declaration [0, 0] - [0, 41]
    (ERROR [0, 9] - [0, 27]
      (identifier [0, 9] - [0, 12])
      (identifier [0, 13] - [0, 18])
      (identifier [0, 19] - [0, 26]))
    (identifier [0, 28] - [0, 37])))
parse_test.swift	0 ms	(ERROR [0, 9] - [0, 27])

Depends on #20, in the sense off it not being too useful without it.