Prevent sql_on_all_attached_db() from indicating success and
simultaneously returning bogus SQL in the case where there are no
attached DBs beyond main or temp -- this does occur in the regression
tests and might occur on an unconfigured system.
require pkgdb_open_multirepos() to have successfully opened at least
one repo database before it can return EPKG_OK.
Add a '-R' option to specify the directory to search for
per-repository configuration files.  This overrides the REPOS_DIR
value set in pkg.conf(5).
Fix tests:

 - AUTODEPS default value is 'yes' nowadays

 - Don't read repository configs from REPO_DIR: testing shouldn't
   know anything about the local pkg config on my build box...
Don't load configs from REPO_DIR while testing.