Review/comment needed for the new public java.util.Base64 class

[Xueming Shen]

Hi

Webrev has been updated with following changes

(1) added a pair of en/decode(ByteBuffer src, ByteBuffer dst) methods
(2) some minor spec clarification regarding the "end of decoding"
(3) performance tuning.

webrev:
http://cr.openjdk.java.net/~sherman/4235519/webrev

some performance scores:
http://cr.openjdk.java.net/~sherman/4235519/score3

-Sherman