fix #427, matching lambdas against variable patterns

[ghost]

Fixes #427.

If you've followed that issue, then there was some discussion about whether the following program should compile or not:

passive class IntContainer
  x: int
  def init(x: int): void
    this.x = x

  def MyCustomPattern(): Maybe int
    Just this.x

class Main
  def main(): void
    match new IntContainer(3) with
      MyCustomPattern(MyCustomPattern) => print MyCustomPattern

How to solve issue #427 depends on whether this example should compile or not. There are some disagreements on this matter and this PR takes the approach which allows the above example to compile, partly because it is easier to implement that way -- the type checker does not have to be extended with the ability to throw a new kind of error.

[ghost]

Also, why the fuck do I keep getting old commits included into my pull requests? I merged upstream/development and checked out a new branch right before making this.

Only the last commit is supposed to be a part of this PR.

[kikofernandez]

Also, why the fuck do I keep getting old commits included into my pull requests? I merged upstream/development and checked out a new branch right before making this.

Drop by my office one of these days and I will get you back on track

[EliasC]

Looks good! Merging in a bit...