Remove obsolete property from ui files

should fix the showing of rotate dialog in GTK+3 build, see https://git.gnome.org/browse/nautilus-image-converter/commit/?id=23441ed6d74b4eba68333c802890cb396721a6d6

Closes https://github.com/mate-desktop/caja-extensions/pull/8
caja-sendto-command: don't leak memory
gajim plugin: don't leak memory
pidgin plugin: various fixes

- add missing spaces (code looked ugly)
- remove a GError variable which has never been used actually
  (and avoid dereferencing NULL pointer at the same time)
- don't leak memory