[Tagging] Key:circuits added to power template

[Ole Nielsen]

As already mentioned in a previous thread I have been drafting a 
definition for a new "circuits" key describing the number of electrical 
circuits of a power line or cable connection. See the feature page at 
http://wiki.openstreetmap.org/wiki/Key:circuits

The new key is mainly intended for underground cable connections 
(power=cable) where the number of cables is unknown or has no fixed 
relationship with the number of electrical circuits.

I have now added this key to the power template expecting nobody will 
have major objections to this additional key. The circuits key will not 
affect current tagging practice. It will however allow mappers to add an 
important extra information to power lines and cables, an information 
that it is not always possible to deduce from the existing cables=* tag.

The circuits=* key is now visible in 
http://wiki.openstreetmap.org/wiki/Key:power and map features.

Ole / polderrunner