Fix incomplete read of uwsgi stats data

... and do that in a way that can be reused by other plugins whose
server side closes the connection when complete. (Not kosher for server
sides that keep the connection open, like memcached; trying to keep
reading would block in that case. So it's off by default, enabled only
by the uwsgi plugin.)

fixes MeetMe/newrelic-plugin-agent#139
Merge pull request #146 from gthb/patch-1

Fix incomplete read of uwsgi stats data