[db-api/configuration] simplify db-api and configuration so that all the connection information is in the repository url, closes #2521848 eg no more specific option of pyro ns host, group, etc. This also fixes broken ZMQ sources. Changes: * dropped pyro-ns-host, pyro-instance-id, pyro-ns-group from client side config, in favor of repository-uri. No migration done, supposing there is **no web-only config** in the wild. Also stop discovering the connection method through the repo_method class attribute of the configuration, varying according to the configuration class. This is a first step on the way to a simpler configuration handling. Notice those pyro options are still available for repository only / all-in-one configurations as they are needed to configure the pyro server. * stop telling connection method using ConnectionProperties, this is so boring. Also, drop _cnxtype from Connection and cnxtype from Session. The former is replaced by a is_repo_in_memory property and the later is totaly useless. * deprecate in_memory_cnx which becomes useless, use _repo_connect instead

import ConfigParser
try:
    undo_actions = config.cfgfile_parser.get('MAIN', 'undo-support', False)
except ConfigParser.NoOptionError:
    pass # this conf. file was probably already migrated
else:
    config.global_set_option('undo-enabled', bool(undo_actions))