Close to defined symbol elimination.


git-svn-id: http://gapt.googlecode.com/svn/trunk/source@1799 85d21ef8-add0-11de-ae77-5bfb9c5a3f34
Implemented the optimization for solvePropositional

git-svn-id: http://gapt.googlecode.com/svn/trunk/source@1801 85d21ef8-add0-11de-ae77-5bfb9c5a3f34