Bug 988689: redirect pref updates to the frozen Nuwa process to its forked child. r=khuey a=1.3+

--HG--
extra : rebase_source : 4b19aba6ec1068dfbba94b18b115138746860608
Bumping manifests a=b2g-bump
Bumping manifests a=b2g-bump
Bumping manifests a=b2g-bump
Merge b2g28 to v1.3t. a=merge