RFR [10] 2018-03-26: Bulk backports to sh/jdk10

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk10-20180326/webrev.01/

This backports last week's work to sh/jdk10:

[backport] Elide Evac-OOM protocol when enqueuing string deduplication candidates in traversal GC
[backport] Remove narrowOop variants of oopDesc::equals and related methods
[backport] Keep track of per-cycle mutator/collector allocs. Fix mutator/collector alloc region
overlap in traversal.
[backport] Rename and cleanup _regions and _free_set uses
[backport] Full GC should not trash empty regions
[backport] Traversal should be reported as concurrent cycle in gc+stats
[backport] Explicit concurrent GC should do traversal when Traversal GC is enabled

Testing: hotspot_gc_shenandoah {fastdebug|release}

Thanks,
-Aleksey