Fix jashkenas#3789: don’t throw a throw (unless it’s in a closure)

Author: GeoffreyBooth

lib/coffeescript/nodes.js

@@ -3258,6 +3258,7 @@ exports.Throw = class Throw extends Base
     if @expression instanceof For or
        @expression instanceof If or
        @expression instanceof Switch or
+       @expression instanceof Throw or
        @expression instanceof While
       fragments = @expression.compileClosure o
     else

src/nodes.coffee

@@ -176,3 +176,9 @@ test "#3709: throwing a while loop", ->
       i++
   catch err
     eq i, 3
+
+test "#3789: throwing a throw", ->
+  try
+    throw throw throw new Error 'whoa!'
+  catch err
+    eq err.message, 'whoa!'