Reported by Thomas Keller, May 27, 2011

The monotone manual still lists get_manifest_cert_trust and 
get_file_cert_trust as valid trust functions for monotone, but 
neither is used in modern monotone anymore.

get_file_cert_trust doesn't even have a reference in 
lua_hooks.{hh,cc} anymore and get_manifest_cert_trust is only used 
during migration from the old manifest format.

We should remove the former trust function in the documentation, 
tests and std_hooks.lua and document for the latter that it is no 
longer actively used in today's monotone, but only when a 
manifest-style db is migrated to the rosters format.