error_limit() function to limit number of error lines per instance

[ktsaou]

This PR adds the function:

error_limit(ERROR_LIMIT *erl, const char *format, ...);

The ERROR_LIMIT *erl parameter can be defined as either global static variable (so that all threads logging will share the same limits) with this:

error_limit_static_global_var(var, log_every_secs, sleep_usecs);

or thread static variable (so that each thread will have its own log limits), with this:

error_limit_static_thread_var(var, log_every_secs, sleep_usecs);

It can be used like this:

            error_limit_static_global_var(erl, 10, 1000);
            error_limit(&erl, "POLLFD: LISTENER: too many open files - used by this thread %zu, max for this thread %zu",
                      p->used, p->limit);

The error_limit() function will:

1. Sleep the defined amount of time, if sleep_usecs is not zero.
2. Lock the global log lock to alter the ERROR_LIMIT *erl members.
3. Respect the flood protection configured by the user.
4. Log the line the caller wants.
5. If the count of messages suppressed is not zero, it will append (repeated %zu times in the last %llu secs)
6. If the sleep time is not zero, it will append (sleeping for %llu microseconds every time this happens)

[thiagoftsm]

PR is working as expected locally. LGTM!