Introduce compatibility with mcl_rubber mod

Closes #1

tools/treetap.lua

@@ -14,6 +14,10 @@
 -- You should have received a copy of the GNU General Public License
 -- along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+if industrialtest.mods.mclRubber then
+	return
+end
+
 local S=minetest.get_translator("industrialtest")
 
 local function onTreetapUse(user,pointed)