RFR JDK-8028397: Undo the lenient mimi decoder suport change (JDK-8025003) in jdk8

[Xueming Shen]

Hi,

The consensus/conclusion from the discussion [1]  regarding the changes we
made earlier for JDK-8025003 [2] is to back out the existing "half-lenient" change
to leave the door open for a clean "lenient" support for future releases.

Here is the webrev for the undo (keep the mime encoder(...) rename change)

http://cr.openjdk.java.net/~sherman/8028397/webrev

Thanks!
-Sherman

[1] http://mail.openjdk.java.net/pipermail/core-libs-dev/2013-November/023048.html
[2] http://hg.openjdk.java.net/jdk8/jdk8/jdk/rev/e7bdb2fcc7bc