lib: Accept leap second in utc_mktime Accept leap second at any time in utc_mktime since utc_mktime is being used before applying the timezone offset everywhere.

Rewrote utc_mktime() so it's now MIT licensed. This also fixes handling years older than 1970. --HG-- branch : HEAD

Changed .h ifdef/defines to use <NAME>_H format. --HG-- branch : HEAD

Fixes to timezone handling which were handling quite badly. added ioloop_timezone which gets updated with ioloop_time. Changed some GMT references to UTC. Timezone offsets are in minutes now everywhere instead of seconds. Fixes for unsigned time_t. --HG-- branch : HEAD