[aarch64-port-dev ] RFR: Import 6 more Shenandoah fixes

[Roman Kennke]

Testing of the last backport and merge has brought up a bunch of fixes
that I would like to get in.

http://cr.openjdk.java.net/~rkennke/aarch64-import-2017-03-06/webrev.00/

It is equivalent to these 6 fixes:

http://mail.openjdk.java.net/pipermail/shenandoah-dev/2017-February/001764.html
http://mail.openjdk.java.net/pipermail/shenandoah-dev/2017-March/001771.html
http://mail.openjdk.java.net/pipermail/shenandoah-dev/2017-March/001783.html
http://mail.openjdk.java.net/pipermail/shenandoah-dev/2017-March/001787.html
http://mail.openjdk.java.net/pipermail/shenandoah-dev/2017-March/001792.html
http://mail.openjdk.java.net/pipermail/shenandoah-dev/2017-March/001796.html

Ok to push?

Roman