[8u] RFR+RFA: 8030993, 8197930, 8170494: Pending JNI exceptions

[Aleksey Shipilev]

This is the bunch of related fixes:
  http://cr.openjdk.java.net/~shade/8030993-8197930-8170494/webrev.8u.01/

*) 8030993: Check jdk/src/share/native/common/jni_util.c for JNI pending exceptions
This one has no public bug, and the only thing we can do is to pick up the actual changeset:
http://hg.openjdk.java.net/jdk/jdk/rev/7a464b795af5 -- it applies cleanly.

*) 8197930: JNI exception pending in initializeEncoding of jni_util.c
This one depends on 8030993. Patch does not apply cleanly, because it expects Compact Strings that
are not available in 8u. Left only "CHECK_NULL(String_init_ID);" from the original patch:
http://hg.openjdk.java.net/jdk/jdk/rev/83fd54252ee4

*) 8170494: JNI exception pending in PlainDatagramSocketImpl.c
The last in the bunch that finalizes the "Pending JNI exception" bug trail. Applies cleanly.

I added jdk8u-fix-request for the last two issues. There is no way to add the label to the first
issue, because the bug is closed, please approve explicitly here.

Testing: hotspot_all, java/lang, java/io, java/nio tests

-- 
Thanks,
-Aleksey