Ambiguous endpoints error could be more informative

One for the wishlist :). For formulas that provide multiple interfaces, as a new user trying to add a relation, the error message could be really helpful and iterate the options without using a list of tuples (or perhaps before the list of tuples):

STR:
Try use add-relation with a formula providing multiple interfaces (eg. `ensemble add-relation postgresql someother`)

ER:
An error message telling me what interfaces I can provide. Something like: "Ambiguous endpoints: Please choose from postgresql:db or postgresql:db-admin. Details: ([(....)])".

AR:
{{{
$ ensemble add-relation ogt postgresql
2011-08-08 17:09:48,558 INFO Connecting to environment.
Ambiguous endpoints: ([(RelationEndpoint(service_name='ogt', relation_type=u'pgsql', relation_name=u'db', relation_role='client'), RelationEndpoint(service_name='postgresql', relation_type=u'pgsql', relation_name=u'db', relation_role='server')), (RelationEndpoint(service_name='ogt', relation_type=u'pgsql', relation_name=u'db', relation_role='client'), RelationEndpoint(service_name='postgresql', relation_type=u'pgsql', relation_name=u'db-admin', relation_role='server'))],)
2011-08-08 17:09:52,201 ERROR Ambiguous endpoints: ([(RelationEndpoint(service_name='ogt', relation_type=u'pgsql', relation_name=u'db', relation_role='client'), RelationEndpoint(service_name='postgresql', relation_type=u'pgsql', relation_name=u'db', relation_role='server')), (RelationEndpoint(service_name='ogt', relation_type=u'pgsql', relation_name=u'db', relation_role='client'), RelationEndpoint(service_name='postgresql', relation_type=u'pgsql', relation_name=u'db-admin', relation_role='server'))],)
}}}