RFR: 8015320: Pull spliterator() up from Collection to Iterable

[Henry Jen]

Hi,

Please review the webrev at

http://cr.openjdk.java.net/~henryjen/ccc/8015320.0/webrev/

This allows turning an Iterable into a stream with spliterator() methods
if the implementation provides one(like many Collection implementations)
rather than be forced to use less-efficient iterator().

Two small changes are not directly related,
- cleanup on SpliteratorCollisions.java test
- add a @see Spliterator for ConcurrentModificationException

Cheers,
Henry