gles/cogl-shader.c: Store the shader type in CoglShader

Nothing was storing the shader type when a shader was created so it
would get confused about whether it was a custom vertex or fragment
shader.

Also the 'type' member of CoglShader was a GLenum but the only place
that read it was treating it as if it was CoglShaderType. This changes
it be CoglShaderType.

cogl/driver/gles/cogl-shader-private.h

@@ -32,7 +32,7 @@ struct _CoglShader
 {
   CoglHandleObject   _parent;
   GLuint             gl_handle;
-  GLenum             type;
+  CoglShaderType     type;
 };
 
 CoglShader *_cogl_shader_pointer_from_handle (CoglHandle handle);

cogl/driver/gles/cogl-shader.c

@@ -69,6 +69,7 @@ cogl_create_shader (CoglShaderType type)
 
   shader = g_slice_new (CoglShader);
   shader->gl_handle = glCreateShader (gl_type);
+  shader->type = type;
 
   return _cogl_shader_handle_new (shader);
 }