Status extras

Added two new metrics to status_detail - data rate and replication lag.

Data Rate is the number of insert / delete / truncate and conflict operations, from syncstats, in the last 5 minutes (as operations per second)

Replication Lag is calculated in two ways:
- the age of the oldest outstanding delta, if there are any outstanding deltas in any of the source databases
- the total_time of the last good syncrun, if there are no outstanding deltas.

e.g.
./bucardo status testsync
======================================================================
Last good                : May 21, 2013 11:44:43 (time to run: 1s)
Rows deleted/inserted    : 0 / 6
Sync name                : testsync
Current state            : Good
...
Data rate (per second)   : insert: 0.10, delete: 0, truncate: 0, conflict: 0
Lag seconds/deltas       : 0.45 / 0
...
======================================================================