Fixed quat mix build

glm/gtc/quaternion.hpp

@@ -74,6 +74,11 @@ namespace detail
 	detail::tquat<T> operator- (
 		detail::tquat<T> const & q);
 
+	template <typename T> 
+	detail::tquat<T> operator+ ( 
+		detail::tquat<T> const & q, 
+		detail::tquat<T> const & p); 
+
 	template <typename T> 
 	detail::tquat<T> operator* ( 
 		detail::tquat<T> const & q, 
@@ -154,7 +159,7 @@ namespace quaternion ///< GLM_GTC_quaternion extension: Quaternion types and fun
 	detail::tquat<T> mix(
 		detail::tquat<T> const & x, 
 		detail::tquat<T> const & y, 
-		typename detail::tquat<T>::value_type const & a);
+		T const & a);
 		
 	//! Returns the q conjugate. 
 	//! From GLM_GTC_quaternion extension.

glm/gtc/quaternion.inl

@@ -156,6 +156,20 @@ namespace detail{
 		return detail::tquat<T>(-q.w, -q.x, -q.y, -q.z);
 	}
 
+	template <typename T> 
+	GLM_FUNC_QUALIFIER detail::tquat<T> operator+
+	( 
+		detail::tquat<T> const & q, 
+		detail::tquat<T> const & p
+	) 
+	{ 
+        return detail::tquat<T>(
+            q.w + p.w,
+	        q.x + p.x,
+	        q.y + p.y,
+	        q.z + p.z);
+	} 
+
 	template <typename T> 
 	GLM_FUNC_QUALIFIER detail::tquat<T> operator*
 	(