Cycles: Support building with latest OSL-1.7dev

So now the following OSL versions are supported (at least for compilation):

- 1.5 with closure alignment patch applied
- 1.6.8 release
- 1.7 development version from latest git

intern/cycles/kernel/osl/emissive.cpp

@@ -77,7 +77,7 @@ public:
 ClosureParam *closure_emission_params()
 {
 	static ClosureParam params[] = {
-	    CLOSURE_STRING_KEYPARAM("label"),
+	    CLOSURE_STRING_KEYPARAM(GenericEmissiveClosure, label, "label"),
 	    CLOSURE_FINISH_PARAM(GenericEmissiveClosure)
 	};
 	return params;