mesa: add support for GL_OES_EGL_image_external

This is an OpenGL ES specific extension.  External textures are textures that
may be sampled from, but not be updated (no glTexSubImage* and etc.).  The
image data are taken from an EGLImage.

Reviewed-by: Brian Paul <brianp@vmware.com>
Acked-by: Jakob Bornecrantz <jakob@vmware.com>

src/mesa/main/shared.c

@@ -108,6 +108,7 @@ _mesa_alloc_shared_state(struct gl_context *ctx)
          GL_TEXTURE_BUFFER,
          GL_TEXTURE_2D_ARRAY_EXT,
          GL_TEXTURE_1D_ARRAY_EXT,
+         GL_TEXTURE_EXTERNAL_OES,
          GL_TEXTURE_CUBE_MAP,
          GL_TEXTURE_3D,
          GL_TEXTURE_RECTANGLE_NV,