receivexlogs: Get rid of old dead receivexlogs
receivexlogs: Get rid of old dead receivexlogs

a) It's a good idea to clean up old dead threads from the background
b) it makes pghoard notice that it's missing a pg_receivexlog for a site
in case a pg_receivexlog process has been killed. (by OOM killer for example)

saaros/pghoard,ohmu/pghoard,ohmu/pghoard,hnousiainen/pghoard,hnousiainen/pghoard