have higher priority

This ensures that only a single set of selector names are exposed and
this is the names which GTK devs consider part of their API. Be a no-op
for older(pre 3.20) versions. Set it with higher priority so it
overrides everything.

Change-Id: I50475ef9f5dd958a1126e6616f4d562eb8e577b5
Signed-off-by: Alexander Kurtakov <akurtako@redhat.com>