Log Message:
Update emacs-snapshot to 24.0.50.20100821.

Changes:
- progmodes/etags.el (tags-file-name): Mark safe if stringp (Bug#6733).
- emacs-lisp/copyright.el (copyright-update-year) (copyright-update):
  Temporary switch-to-buffer to ensure the buffer change being queried
  is visible (Bug#5394).
- font-lock.el (lisp-font-lock-keywords-2): Add
  combine-after-change-calls, condition-case-no-debug,
  with-demoted-errors, and with-silent-modifications (Bug#6025).
- progmodes/compile.el (compilation-error-regexp-alist-alist): Give
  the Ruby rule a lower priority than Gnu (Bug#6778).
- mouse.el (mouse--drag-set-mark-and-point): New function.
  (mouse-drag-track): Use LOCATION arg to push-mark.  Use
  mouse--drag-set-mark-and-point to take click-count into
  consideration when updating point and mark (Bug#6840).
- net/rcirc.el (rcirc-log-process-buffers): New option.
  (rcirc-print): Use it.
  (rcirc-generate-log-filename): New function.
  (rcirc-log-filename-function): Change default to
  rcirc-generate-log-filename (Bug#6828).
- term/ns-win.el (ns-get-pasteboard, ns-set-pasteboard):
  Use QCLIPBOARD instead of QPRIMARY (Bug#6677).
- image.el (create-animated-image): Don't add heuristic mask to image
  (Bug#6839).
- files.el (locate-file-completion-table): Only list the .el and .elc
  extensions if there's no other choice (bug#5955).
- cus-edit.el (custom-group-value-create): Add extra newline
  before end line (Bug#6876).