Build errors should appear as markers in the editor

[dragos]

For instance, this code generates a build error:

object test {
  var foo = bar

  def bar = 0                                  
}

However, the build error appears only in the Problem View, and not in the editor.

[dragos]

There is a deeper problem: build errors are reported against the instrumented source. In order to map back the position to the original worksheet, we need some help. Probably the list of patches would be enough.