Update lib/carbon/aggregator/buffers.py

Closing MetricBuffers after all interval buffers are outside the age threshold.
carbon.conf: Add [aggregator] WRITE_BACK_FREQUENCY
Merge pull request #50 from jdanbrown/write-back-frequency

carbon.conf: Add [aggregator] WRITE_BACK_FREQUENCY
Fix relay's per-destination instrumentation
use global event handlers properly in client.py
added warning if the aggregator is misconfigured
caron(-aggregrator) will substitute a timestamp of 0 with the current time, to enable time synchronised stats
Clean up the code a bit in the example client
Remove a bit of unnecessary code
Add carbon.exceptions

For now, this only contains CarbonConfigException, but we can add
more later down the road depending on what types of failure conditions
we want to gracefully handle and report. I see a lot of ceres related
potential here.
Update carbon.conf and it's unit tests for the new exception

Also silence an annoying DeprecationWarning when running the tests
Update daemons to use new exceptions and gracefully print them
Updating test to not use deprecated e.message
Changed special timestamp '0' to '-1'
The length of the carbon-relay's per-destination queue is not visible.

This patch adds
carbon.relays.<hostname>.destinations.<dest-host>.relayMaxQueueLength,
a counter that records the maximum queue length for that destination
during the reporting period.
Remove an un-needed attempt to send a instrumentation stat.
Merge pull request #90 from pcn/add-relay-queue-stat

The length of the carbon-relay's per-destination queue is not visible.
Merge pull request #58 from gwillem/master

Substitute input timestamp of "-1" to time.time() on carbon server
Merge pull request #63 from SEJeff/handle-config-errors

Handle config errors a bit more gracefully
Merge pull request #65 from lbosson/master

Closing MetricBuffers after all interval buffers are outside the age threshold.