Sprites turn white after a while about quipkit HOT 1 CLOSED

Keep sdlgl.texture ref in sprite.lua. Closed by 7fd9dfc.

• The problem was that the OpenGL texture ID is only valid as long
  as the sdlgl.texture object was 'live'. The sprite object didn't
  keep a ref to it, so it got GC'd, causing the __gc finalizer to
  be called, which deletes the texture, causing the white block.
• sfont.lua also grabs the tex ID from an sdlgl.texture, but it
  keeps the object around, so it doesn't suffer the same problem.

from quipkit.