Add -M (measure-mode), where master client only opens 1 connection per thread (to avoid client-side queuing delay).
1. Implemented --measure_* options to reasonably separate
configuration of measurement client (mutilate master) from
load generating clients (mutilate agents).  Use -C and
--measure_depth to approximate open-loop measurement control
(i.e. so long latency requests don't screw up the sample
population), and use -Q to ensure that you see minimal
client-side queuing delay.

2. Quickly documented agent "protocol".  Lots of improvement
to be had here...
Clean out some dead code.
Add --skip option: By default, mutilate tries to maintain a long-term QPS average by issuing requests as quickly as possible until it catches up with where it 'ought' to be.  If you give the --skip option, it will instead just skip sending requests that are already late.
Minor beautification.
--skip: pass option with options_t to agents
Change --skip behavior to only jump ahead if the tx time is at least 5ms (hardcoded for now) behind.  Always pacing with timer events was causing it to severely miss QPS targets...
Updated sync_agent() to be less ridiculous.  Still ridiculous, though.