RFR: Fixed two string dedup issues

[Roman Kennke]

Am 09.10.2017 um 18:45 schrieb Zhengyu Gu:
> Fixed two issues:
>
> 1) Missing string dedeup on shenandoah write barrier fast path.
>
> 2) Missing dedup table reference update on piggyback reference update 
> path.
>
>
> Webrev: 
> http://cr.openjdk.java.net/~zgu/shenandoah/strdedup_fix/webrev.00/
>
> Test:
>   hotspot_gc_shenandoah fastdebug and release on x64 and aarch64.
>
> Thanks,
>
> -Zhengyu

Looks good to me!