Clean up queue_replace.
Clean up queue_replace.

There are a fair few references involved here, so be careful.  Both
the queue and the old glyph retain references to the new glyph, and
the queue releases its reference to the old glyph.

epronk/xtickertape,tphelps/xtickertape,tphelps/xtickertape,epronk/xtickertape,tphelps/xtickertape