validator should search for nearby roads on unconnected roadends

[openstreetmap@…]

when validating osm data in none home regions, you often can find some users (mainly using merkaartor and sometimes potlatch) who did not realize that their data may look fine when rendered, but is useless for routing, as their roads are not connected.
as this should be handled properly by the editor in the first place (some kind of snapping - potlatch does this (maybe not aggressive enough) , but merkaartor seems to ignore this problem completely), we already have a lot of existing data with these errors.

i would propose a validator scheme that checks the following when the highway tag is set:

• test if both lineends are connected to another road: yes => end; everything is ok
  
• test of both lineends are unconnected: yes => end; error (list road in validator results)
  
• test if there is another road (line between two nodes) within close proximity of the unconnected end of the highway: yes => end; warning (list end node and proximal road in validator results)

i know the last test is very cpu-intensive (maybe there should be done any elimination tests, if a way is in close reach of the unconnected node) and not very easy to implement, but we will get a much better quality of our data. maybe the intersecting test could be a starting point for conding.

currently this could only be done by visual (and therefore time consuming) visual inspection of suspicious regions and users which have a lot intersecting ways (the other thing that happens, when roadends are placed not correctly)

[stoecker]

Implemented a little bit different in newest validator.