Fix an ORTE -> OPAL name change that was missed in r29530.
Output the directory where the java files were found.

Useful for debugging / understanding exactly where OMPI will be using
Java header files / libraries from.
Add an Open MPI-specific comment here so that we hopefully don't lose
this change the next time we update libevent.

cmr=v1.7.4:ticket=3882
Add a 1.7.4 bullet about the libevent header file regression