Updated chat/libpurple to 2.5.1

  libpurple:
    * In the Join/Part plugin, add the ability to apply the rules to
      buddies.  By default, joins and parts for buddies are still shown.
    * Support SOCKS proxies specified in GNOME or Windows proxy settings.
    * Fix some possible crashes in MSNP15.
    * Enable a default SSL trust relationship for MSN servers.
    * Avoid disconnecting from XMPP servers on parse errors that are
      non-fatal.
    * Include some perl files that were mistakenly omitted in 2.5.0.

  Pidgin:
    * Prevent use of custom smilies without "shortcuts."
    * Fix a crash that could appear with AIM buddy tooltips.

  Artwork:
    * General refresh of many icons in the interface.
    * Many cleanups to artwork source are now included in the distribution.
    * A new "throbber" animation has been added to indicate when accounts
      are connecting.

(abs)