allow source:maxspeed=PL:zone40

[mkoniecz]

What steps will reproduce the problem?

1. tag zone 40 maxspeed in Poland with maxspeed=40 and source:maxspeed=PL:zone40 what AFAIK is correct
2. run validator

What is the expected result?

No complaints about source:maxspeed=PL:zone40

What happens instead?

Unknown source:maxspeed context: zone40 (1)

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

​https://www.openstreetmap.org/way/22690910#map=19/50.08515/19.97966

URL:https://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2018-06-24 19:57:43 +0200 (Sun, 24 Jun 2018)
Build-Date:2018-06-24 18:08:53
Revision:13974
Relative:URL: ^/trunk

Identification: JOSM/1.5 (13974 en) Linux Ubuntu 16.04.4 LTS
Memory Usage: 812 MB / 869 MB (339 MB allocated, but free)
Java version: 1.8.0_171-b11, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
Screen: :0.0 1920x1080
Maximum Screen Size: 1920x1080
Dataset consistency test: No problems found

Plugins:
+ OpeningHoursEditor (34095)
+ buildings_tools (34212)
+ continuosDownload (1529090613)
+ imagery_offset_db (34337)
+ reverter (34271)
+ todo (30304)

Last errors/warnings:
- W: Invalid jar file ''<josm.userdata>/plugins/imagery_offset_db.jar.new'' (exists: false, canRead: false)
- W: No configuration settings found.  Using hardcoded default values for all pools.
- E: Skipping to the next rule, because of an error:
- E: org.openstreetmap.josm.gui.mappaint.mapcss.parsergen.ParseException: Encountered " <IDENT> "way "" at line 222, column 1.

[Don-vip]

In 13976/josm:

fix #16425 - support "zone40" maxspeed context