RFR(s): 8152617 add missing wildcards to Optional or() and flatMap()

[Stuart Marks]

Hi all,

Please review this small API adjustment to Optional.or and flatMap to add 
wildcards. This provides a bit more flexibility to callers about the types of 
functions they can provide to these methods.

The or() method is new in 9 so there is no compatibility issue.

The flatMap() method was introduced in 8, so this is a change to an existing 
API. There shouldn't be a binary compatibility issue, since the method's erasure 
doesn't change. I *think* it is source compatible, as anything that was accepted 
by the old signature:

     flatMap(Function<? super T, Optional<U>> mapper)

should also be accepted by the new signature:

     flatMap(Function<? super T, ? extends Optional<? extends U>> mapper)

But there may be some subtle issues of which I'm unaware.

Bug report:

	https://bugs.openjdk.java.net/browse/JDK-8152617

Webrev:

	http://cr.openjdk.java.net/~smarks/reviews/8152617/webrev.0/

Thanks,

s'marks