fail bootstrap early with wrong jdk

[Bill Dudney]

I think we should fail the bootstrap early if using jdk 1.5 as well  
as failing the maven build.

http://issues.apache.org/jira/browse/GERONIMO-2403
has a patch attached that works, but there might be a way to reuse  
the mojo that Jason wrote, not sure...

Thanks,

-bd-