Fix format.

  From clang:

  extsmaild.c:1435:32: warning: format specifies type 'int' but the argument has type 'time_t' (aka 'long') [-Wformat]
        printf("%d seconds\n", external->timeout);
                ~~             ^~~~~~~~~~~~~~~~~
                %ld

  I like this compiler.
Use -Wextra.
Fix signed vs unsigned comparisons.
Do not warn about unused parameters.
Unused parameter in signal handlers.
Remove unused parameter in read_argv().
Remove unused parameter in find_group().
Remove unused parameter in try_groups().
Remove unused parameter in do_notify_success_cmd().
Make static those things which can be static.
Remove undefined function rdline().
Initialise yycin.
Initialise conf.