* THANKS: spelling fixes.

  * configure.ac:
    + Added curly braces around variables.
    + Got rid of the "x$foo" constructs.
    + Renamed *_plugin conditionals into *_p.
  * debian/changelog:
    + Fixed a duplicate entry.
    + Added an entry for an old Debian upload that fixed #117180.
  * debian/control:
    + Added a build dependency on libimlib2-dev for skins.
  * debian/rules:
    + Activated support for skins.