Store float values in an union.

Single variable cannot have many values of different types. This also saves some memory, because union allocates memory just for one of its members.

engine/api.c

@@ -1217,7 +1217,7 @@ double ph7_value_to_double(ph7_value *pValue) {
 	if(rc != PH7_OK) {
 		return (double)0;
 	}
-	return (double)pValue->rVal;
+	return (double)pValue->x.rVal;
 }
 /*
  * [CAPIREF: ph7_value_to_string()]
@@ -1792,7 +1792,7 @@ int ph7_value_null(ph7_value *pVal) {
 int ph7_value_double(ph7_value *pVal, double Value) {
 	/* Invalidate any prior representation */
 	PH7_MemObjRelease(pVal);
-	pVal->rVal = (ph7_real)Value;
+	pVal->x.rVal = (ph7_real)Value;
 	MemObjSetType(pVal, MEMOBJ_REAL);
 	return PH7_OK;
 }