Miscellaneous tq-related fixes.

Miscellaneous tq-related fixes.

* lisp/emacs-lisp/tq.el: Small grammar fix in comments.
  (tq-enqueue): Check for existence of queue rather than the head queue
  item's question, which was a no-op.
  (tq-filter, tq-process-buffer): Make sure the process buffer exists
  before making it the current buffer.

* lispref/processes.texi (Transaction Queues): Remove stray quote
  character.

Revision: emacs@sv.gnu.org/emacs--devo--0--patch-411
Creator:  Michael Olson <mwolson@gnu.org>