Rewrite property calls

Property calls are treated by the compiler in a special manner - the
callee gets a receiver object - hence we should end up with an
instrumented expression, which also contains an analoguos property
call.

Call of a property is instrumented like:

    o.f(e0, e2, ..., en)
    =>
    (function($a0, $a1, ..., $an, $obj, $key) {
      ER_readProp($obj, $key, $obj.$key);
      return $obj.$key($a0, $a1, ..., $an); })
    (e0, e1, en, ..., o, f)