implemented #284
busy_workers and idle_workers must be GAUGE
use uwsgi.start_tv for srand instead of recomputing it
completed metric threshold subystem
do not destroy the stats pusher loop on EINTR
added stats pusher default plugins
metrics as objects in stats subsystem
Support HTTP Status 509

Whilst this isn't an official RFC, it's documented on e.g. Wikipedia. http://en.wikipedia.org/wiki/List_of_HTTP_status_codes#5xx_Server_Error
Merge pull request #447 from flavour/master

Support HTTP Status 509
added metric api to ruby
prepare for uWSGI 1.9.19
fixed template plugin
more plugins for coveriti, fixed gccgo
improved gccgo plugin
moved go to broken plugins
try to address EAGAIn body read problem
metrics: add missing exit on error path

Fixed null pointer dereference.

Reported by Coverity as CID #1127337
plugins/servlet: Check uwsgi_jvm_exception return value

Reported vy Coverity as CID #1125169.
plugins/xslt: fix memory leak

Reported by Coverity as CID #1125168
plugins/xslt: fail early if content_type is null

Fixes null pointer dereference.

Reported by Coverity as CID #1125161