Build links the right way.
This also involved dropping that leading slash on the osm_default_icon.
And since it would require changing the old osm_tag_icons too,
I just removed that relic.
It just didn't work, but also, it didn't use writefile, which is not
desirable for security. Fixed both issues.
Also removed some unnecessary debug messages.
Add an underlay for the osm plugin.
Update links to right path to icon. Note that the osm plugin has a
pervasive bug in how it links to icons; it assumes the site is at /.
I did not attempt to fix that; it should be using urlto() to make a correct
relative link.
Joey Hess
Antoine Beaupré