list allowed values for ldap protocol setting in help, so that the generated file includes this in a comment
[system]
db-driver = sqlite
db-host =
adapter = native
db-name = tmpdb
db-encoding = UTF-8
db-user = admin
db-password = gingkow
[extern]
adapter = pyrorql
pyro-ns-id = extern
cubicweb-user = admin
cubicweb-password = gingkow
mapping-file = extern_mapping.py
base-url=http://extern.org/
[extern-multi]
adapter = pyrorql
pyro-ns-id = extern-multi
cubicweb-user = admin
cubicweb-password = gingkow
mapping-file = extern_mapping.py
[admin]
login = admin
password = gingkow