RFR: JDK-8008386 (cs) Unmappable leading should be decoded to replacement.

[Xueming Shen]

Sean,

Here is the forward port for the jdk8 repo, please help review.

http://cr.openjdk.java.net/~sherman/8008386/webrev/

All regression tests passed. The reg test TestIBMBugs.java is updated to
follow the new rule for the unmappable leading byte. Your original reg
test has been updated to remove the bugLevel=1.5 stuff.

Thanks!
-Sherman