lk rules throw more helpful error messages now, bug fixes to definition elminiation

git-svn-id: http://gapt.googlecode.com/svn/trunk/source@1767 85d21ef8-add0-11de-ae77-5bfb9c5a3f34
Adding an exporter for verit.

git-svn-id: http://gapt.googlecode.com/svn/trunk/source@1768 85d21ef8-add0-11de-ae77-5bfb9c5a3f34