[RFC] default HTCP

[Amos Jeffries]

With HTTP/1.1 functionality Variants are much more common and the ICP 
failure rate is growing quite high.

I propose altering the default behaviour of peering to using HTCP 
queries by default.

This would entail adding "htcp=off" and "icp" options to cache_peer and 
altering the build defaults such that HTCP was always available.
The "no-query" option is vague enough that it can be left with its 
existing behaviour modified to disable the default queries.

Amos