FindJava: Do not accept OS X stub 'java' as Java

OS X provides a stub 'java' to inform callers that Java is not present.
When checking the 'java -version' output, look for such a message and if
found pretend 'java' was not found.

Suggested-by: Sean McBride <sean@rogue-research.com>
Merge topic 'FindJava-no-osx-stub' into next

dd378258 FindJava: Do not accept OS X stub 'java' as Java