implement Root[] for If[0<x<10,f]

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@37955 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
redo r37928 Don't check if the var itself is undefined (maybe undefined at last compute)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@37956 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
better place for 3D

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@37957 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e