[Tagging] barrier enforcing maxwidth

[Carl von Einem]

johnw wrote on 08.09.15 05:38:
> (...)
> https://goo.gl/maps/8KUw7  The maxwidth is signed and guardrails are
> doing the job. This is width limited for the very narrow bridge in the
> background.

barrier=guard_rail
maxwidth=2.2
traffic_sign=maxwidth

> https://goo.gl/maps/3NT9X  The other direction. Poles are used.

see https://wiki.openstreetmap.org/wiki/Tag:barrier%3Dbollard

barrier=bollard
maxwidth=2.2 (should be the same width as above)
motor_vehicle=yes (to be set in this case since bollard implies "no" by 
default)