Change a test case: configuration options are now case sensitive.
Fix config file load and parse logic in conf.c, always copy 'debug' flags
from config.debug.
The config schema 'interfaces' option is no longer MANDATORY.
Introduce new CLIFLAG_PERMISSIVE_CONFIG to supress bad-config ERROR messages
from the 'config set' and 'config get' commands.
Refactor cli_execute() into cli_parse() and cli_invoke(). Use *const* struct
command_line_option everywhere.
This requires building with _GNU_SOURCE to get access to struct ucred on Linux. Previously the test failed on every platform except glibc <2.8 or so.
Building with _GNU_SOURCE causes TRUE to be defined so we can't use this as a variable anymore, and MIN/MAX so don't define our own.
