Unbreak discovery from 0.9.38.

'Whoops'. _jython_aware_splitext was not defined accurately
enough and broke outside of the testing context.

Change-Id: I4d6a421b90515b24c0f4ad08b5db818b8fec6fe9
Opening 0.9.40 for development.

Change-Id: I992a7f86c2edd2bf65bdfc89dbd6cd2689e96fb5