[giac] #3393 add Invert[ <Function> ]

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@26046 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
[giac]  minus {pi} not needed in lname() any more

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@26047 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e