Added end to end message latency calculations

This commit adds new statistics about how long individual messages take
from being published to being finished.  We maintain several percentile
values, the exactly quantiles which can be specified as runtime
parameters to nsqd.  In addition, this information is displayed quite
shnazily in nsqadmin.
Merge pull request #280 from mynameisfiber/master

nsqd: track stats of end-to-end message processing time
bump 0.2.24-alpha
nsqadmin: fix aggregation on e2e graphs
Merge pull request #281 from mreiferson/e2e_graphs_281

e2e aggregrate graphs bug
use latest Godeps
tweak README
add moz to README
apps: refactor reader command line options

this removes the individual reader command line flags in favor
of a single --reader-opt flag (that can be specified multiple times)
and passes through the value to nsq.Reader using the new reader.Configure().

nsq_to_file:
    * deprecated --gzip-compression in favor of --gzip-level
    * deprecated --verbose in favor of --reader-opt=verbose

nsq_to_http:
    * deprecated --throttle-fraction in favor of --sample
    * deprecated --http-timeout-ms in favor of --http-timeout (which is a
      duration flag)
    * deprecated --verbose in favor of --reader-opt=verbose
    * deprecated --max-backoff-duration in favor of
      --reader-opt=max_backoff_duration=X

nsq_to_nsq:
    * deprecated --verbose in favor of --reader-opt=verbose
    * deprecated --max-backoff-duration in favor of
      --reader-opt=max_backoff_duration=X
bump Godeps for go-nsq to v0.3.4
add go1.2 to travis
Merge pull request #267 from mreiferson/snappy_apps_267

apps: compression support
simplify godep usage
bump v0.2.24 stable
nsq_tail: add -n to limit the number of messages
Merge pull request #285 from elubow/nsq_tail_update

nsq_tail: add -n to limit the number of messages
nsqd: Adding sample_rate at the client level
Merge pull request #286 from elubow/channel_sampling

nsqd: channel sampling
bump 0.2.25-alpha
do not block when n = 0