Validation of attributes

[lhstrh]

Currently, it is possible to annotate using attributes in ways that are inconsistent. For instance, one could write something like:

  reactor Source {
  output out: int
  timer t(1 nsec, 10 msec)
  state s: int = 0

  @label(value="Foo")
  @label(value="Bar")
  reaction(startup) {= lf_print("Starting Source"); =}
}

The validator should flag the second @label as inconsistent with the first.