Fix for __decorate emit on undecorated file following a decorated file

Author: rbuckton

src/compiler/checker.ts

@@ -10867,6 +10867,8 @@ module ts {
                 checkGrammarSourceFile(node);
 
                 emitExtends = false;
+                emitDecorate = false;
+                emitParam = false;
                 potentialThisCollisions.length = 0;
 
                 forEach(node.statements, checkSourceElement);

tests/cases/conformance/decorators/class/decoratedClassFromExternalModule.ts

@@ -0,0 +1,9 @@
+// @target: es6
+// @Filename: decorated.ts
+function decorate() { }
+
+@decorate
+export default class Decorated { }
+
+// @Filename: undecorated.ts
+import Decorated from 'decorated';