Use a chain of "else if" statements, drop known_opt completely.
Added bonus: We stop trying to parse option arguments as (possible) options.

Arguments of -u/-g and path options (-conf) now check whether their argument
starts with a dash ('-') and error out in case it does (= next option, not a valid argument).

Use PATH_MAX for everything that stores files / directories.

Use switch_bool_t and SWITCH_TRUE/_FALSE for boolean variables.

Use EXIT_SUCCESS/_FAILURE for exit() calls.

Get rid of excessive indenting (especially in the win32 parts of main()).

NOTE: Win32 parts untested.
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>