Resolves #1142.

Example showing correctness of existing "missing class member":

module Foobar where

class Foobarable m where
  foobar :: m
  oops :: m

data Blah = Beanz | Spaz

newtype Fooample = Fooample Blah

instance foobarableFooample :: Foobarable Fooample where
  foobar = Fooample Beanz

Errors with:

Error:
Error in type class instance Foobar.Foobarable Foobar.Fooample:
Error at /home/michael/dev/contrib/Foobar.purs line 11, column 1 - line 12, column 21:
Member oops has not been implemented
See https://github.com/purescript/purescript/wiki/Error-Code-MissingClassMember for more information, or to contribute content related to this error.

Example showing new error:

module Foobar where

class Foobarable m where
  foobar :: m

data Blah = Beanz | Spaz

newtype Fooample = Fooample Blah

instance foobarableFooample :: Foobarable Fooample where
  foobar = Fooample Beanz
  oops = Fooample Spaz

Errors with:

Error:
Error in type class instance Foobar.Foobarable Foobar.Fooample:
Error at /home/michael/dev/contrib/Foobar.purs line 12, column 3 - line 12, column 19:
Member oops does not belong to the class being instantiated
See https://github.com/purescript/purescript/wiki/Error-Code-ExtraneousClassMember for more information, or to contribute content related to this error.