Fix type inferencing and syntax highlighting for dynamic variable set within if and else blocks

[eric-milles]

Consider the following:

File findFile(boolean condition) {
  def file
  if (condition) {
    file = new File(System.getProperty('user.home'), '.groovy')
  } else {
    file = new File(System.getProperty('groovy.root'))
  }
  file.canonicalFile
}

The last occurrence of "file" is showing as unknown (underlined). Since the variable is initialized to a java.io.File in both conditional branches, the type should propagate to the outer block.

[eric-milles]