hide the previous toolpaths after generating a new one, if there was only one visible before (this should be less confusing)
display the number of current toolpaths in the toolpath tab label


git-svn-id: https://pycam.svn.sourceforge.net/svnroot/pycam/trunk@191 bbaffbd6-741e-11dd-a85d-61de82d9cad9