[engine/input] Re-enable mouse button parameter bindings

Re-enable the possibility to define custom mouse actions by binding
commands to "<alias|module>.<left-click|right-click|...>". These
commands are then executed as shell commands.

fixes #30

runtests.sh

@@ -1,13 +1,11 @@
 #!/bin/sh
 
-test=$(which nosetests)
-
 echo "testing with $(python2 -V 2>&1)"
-python2 $test --rednose -v tests/
+python2 $(which nosetests) --rednose -v tests/
 
 if [ $? == 0 ]; then
 	echo
 
 	echo "testing with $(python3 -V 2>&1)"
-	python3 $test --rednose -v tests/
+	python3 $(which nosetests-3) --rednose -v tests/
 fi