Fix the context class for continuations in closures

The late static bound class was being used for the context. This
was wrong, but before this change there was no context at all, so
it would have taken newly written code to expose the bug.

However, a given continuation can be instantiated from a large number
of different lsb classes (but only one context class) which meant that
we got an explosion of unnecessary translations.

hphp/runtime/vm/bytecode.cpp

@@ -6702,7 +6702,7 @@ VMExecutionContext::createContinuation(ActRec* fp,
     Class* cls = frameStaticClass(fp);
 
     if (origFunc->isClosureBody()) {
-      genFunc = genFunc->cloneAndSetClass(cls);
+      genFunc = genFunc->cloneAndSetClass(fp->m_func->cls());
     }
 
     if (obj.get()) {