fix graphite for default prefixes & gauges

* use per-metric type (ie: gauge vs counter) graphite prefixes
Merge pull request #139 from jehiah/graphite_gauges_139

Two missing Grahite graphs in nsqadmin on v0.2.16
nsqadmin: fix redirects

* PostParams.Get non-errors
* better handling of empty params
docs: correct MPUB documentation
Merge pull request #138 from mreiferson/nsqadmin_rd_138

nsqadmin: action redirects bug
Merge pull request #140 from mreiferson/mpub_docs_140

MPUB protocol spec
handle gzip revisions (don't append existing files)
Merge pull request #129 from jehiah/gzip_revision_129

nsq_to_file: don't append existing gzip files
nsqd/nsqlookupd: simplify protocol magic handling
nsqd/nsqlookupd: forceably close connections on invalid magic
nsqlookupd: improve reliability of tests
nsqd: fatal errors and responses

* SUB / IDENTIFY now have success responses
* all errors except for FIN / REQ commands are fatal
* invalid RDY count values are now fatal
* simplified set of error codes
* add context to error frames
update ChangeLog and upgrade notes