Ignore STAY_OFF_MY_LAWN when setting JAVA_HOME.

Don't check STAY_OFF_MY_LAWN in set_java_home.  That function already
refuses to update JAVA_HOME if it's set to something, which should
be sufficient for anybody who doesn't want the script to mess with it.

With this change, you can get the benefits of the 1.5/1.6 auto-selection
without having to suffer through window title changes.

Change-Id: I5cfc5d6fdf26a10b42b52925f877012c0506b9a5