Call glClientActiveTexture() through COGL context.

Fixes build issues on systems with OpenGL header older than 1.3.

common/cogl.c

@@ -48,6 +48,10 @@ typedef CoglFuncPtr (*GLXGetProcAddressProc) (const guint8 *procName);
 #include "cogl-gles2-wrapper.h"
 #endif
 
+#ifdef HAVE_COGL_GL
+#define glClientActiveTexture ctx->pf_glClientActiveTexture
+#endif
+
 #ifdef COGL_GL_DEBUG
 /* GL error to string conversion */
 static const struct {

gl/cogl-primitives.c

@@ -37,6 +37,8 @@
 
 #define _COGL_MAX_BEZ_RECURSE_DEPTH 16
 
+#define glClientActiveTexture ctx->pf_glClientActiveTexture
+
 void
 _cogl_path_add_node (gboolean new_sub_path,
 		     float x,