String.lastIndexOf confused by unpaired trailing surrogate

[Martin Buchholz]

I've added another mini-patch to my patch set.

http://cr.openjdk.java.net/~martin/webrevs/openjdk7/isBMPCodePoint3

This deletes Surrogate.java, as Ulf wants,
except that ... it's another variant of Surrogate.java!
(which I didn't know existed)

Uses of Surrogate.neededFor are all now changed to
Character.isSupplementaryCodePoint, as suggested by Ulf.

I intend to fold all of the isBMPCodePoint patches together into one
before I commit them.

Ulf, please review.

Martin