TreeGrammarDecomposition: fixed 2 bugs leading to wrong keys in cases where n>=2

git-svn-id: http://gapt.googlecode.com/svn/trunk/source@2107 85d21ef8-add0-11de-ae77-5bfb9c5a3f34
TreeGrammarDecomposition: fixed a bug leading to wrong rests (by avoiding to take restfragments between newly and previously introduced non-terminals)

git-svn-id: http://gapt.googlecode.com/svn/trunk/source@2108 85d21ef8-add0-11de-ae77-5bfb9c5a3f34