[Patch] Validator: Warn when *:{backward|forward}=* appears with oneway=!no

[Am909]

When splitting a way into a dual carriageway, it's possible to overlook the fact that there are *:{backward|forward}=* tags (e.g. source:maxspeed:forward) that need special handling.

Please add a warning to the validator to check for any forward/backward tags when the oneway key is present and its value is not "no".

[simon04]

The attached patch should provide the desired warning. Additionally, the description of the validator file format is clarified.

[stoecker]

In [4295/josm]:

fix #5844 - patch by simon04 - Validator: Warn when *:{backward|forward}=* appears with oneway=!no

[simon04]

In [4397/josm]:

fix #6760, see #5844 - remove validator warning "oneway combined with *:backward/forward" as it causes false positives