Config is now base class for all configurations...

...main Roundup configuration class is CoreConfig.

Builtin TRACKER_HOME renamed to HOME in Config and Options.
In CoreConfig, TRACKER_HOME is an alias for HOME.

Option.value2str(): added parameter 'current' -
stringify current Option value.

Option RDBMS_PORT defaults to None.

Config: added methods add_section, update_option, getopt (not implemented).

Config.save(): added warning about unset options at the top of the file.

new class UserConfig for inifile-driven configs.

CoreConfig: new attributes .ext and .detectors holding UserConfigs
for extensions and detectors, respectively.

Author: Alexander Smishlajev