Allow oneway=yes in route relations

[Hufkratzer]

What steps will reproduce the problem?

1. Load a route relation wirh "oneway=yes", e.g.

​http://www.openstreetmap.org/relation/1158932 hiking
​http://www.openstreetmap.org/relation/4007549 hiking
​http://www.openstreetmap.org/relation/4007549 hiking
​http://www.openstreetmap.org/relation/2910040 hiking (from closed https://josm.openstreetmap.de/ticket/9992)
​http://www.openstreetmap.org/relation/1625564 foot
​http://www.openstreetmap.org/relation/179634 running
​http://www.openstreetmap.org/relation/4052912 horse
​http://www.openstreetmap.org/relation/6010915 piste
​http://www.openstreetmap.org/relation/414663 piste

2. Execute the validator

What is the expected result?

The validator should allow oneway=yes in route relations without complaint

What happens instead?

The validaor gives a warning: "oneway without highway or railway"

Please provide any additional information below. Attach a screenshot if possible.

Page ​http://wiki.openstreetmap.org/wiki/Hiking#Tags_of_the_relation says:
"optional) Use oneway=yes to indicate that the route is to be walked in only one direction, according to the signposts on the ground"

Page ​http://wiki.openstreetmap.org/wiki/Key:oneway says: "use on relations unspecified".

Corresponding discussion in repository of waymarkedtrails.org:
​https://github.com/lonvia/waymarked-trails-site/issues/202

I see no need for a warning here, it's rather confusing; what else should one use in such cases?

Compare https://josm.openstreetmap.de/ticket/9992 (closed)

URL:http://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2016-04-28 12:48:16 +0200 (Thu, 28 Apr 2016)
Build-Date:2016-04-28 10:51:36
Revision:10161
Relative:URL: ^/trunk

Identification: JOSM/1.5 (10161 en) Windows XP 32-Bit
Memory Usage: 162 MB / 989 MB (43 MB allocated, but free)
Java version: 1.7.0_80-b15, Oracle Corporation, Java HotSpot(TM) Client VM
Dataset consistency test: No problems found

Plugins:
- PicLayer (32158)
- apache-commons (32158)
- routes (32158)
- scripting (30722)

Tagging presets:
- https://josm.openstreetmap.de/josmfile?page=Presets/NewTags&zip=1

Map paint styles:
- https://josm.openstreetmap.de/josmfile?page=Styles/MTB&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Surface&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Surface-DataEntry&zip=1

[Klumbumbus]

In 10350/josm:

fix #12942 - improve oneway warning