core: Timeout on switching back to a pool after a broken connection lowered from 5 minutes to one minute.
log: Added a switch to the log date and time format.

It is possible to switch back to full date and time on each log line with "--log-dateformat 1". The short time-only format is default with the value of 0.

Log with short time-only format looks like:
 [23:59:59] Accepted 389c47d1 Diff 1.16K/512 GPU 0 pool 0
 [00:00:16] Log date is now 2013-12-22
 [00:00:16] Stratum from pool 0 detected new block
 [00:00:33] Accepted 7a4950a4 Diff 536/512 GPU 0 pool 0
log: Change log_dateformat to log_show_date and make it bool.
log: Do not pad log string with a space.