hg: shenandoah/jdk: Fix deduplication assert and update comments

[zgu at redhat.com]

Changeset: 42505c64f1c7
Author:    zgu
Date:      2018-10-03 12:14 -0400
URL:       http://hg.openjdk.java.net/shenandoah/jdk/rev/42505c64f1c7

Fix deduplication assert and update comments

! src/hotspot/share/gc/shenandoah/shenandoahStringDedup.cpp