Fixes to the Solar Sysytem tab of the options dialog.  Child widgets of
the "Show asteroids" and "Show comets" checkboxes are disabled when the
boxes are unchecked.  Also, the "Clear All Planet Trails" button finally
works again.  It will not clear the temporary trail attached
automatically to a solar system body when it is centered; it only removes
trails which were manually added in the popup menu.

svn path=/branches/KDE_3_3_BRANCH/kdeedu/kstars/; revision=342889