Fix for #4693, also xx+yy=1 working again

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@37206 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Fix for #4693: make sure we compute the power

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@37207 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e