Honour SX_DEBUG_SINGLEHOST on block uploads too
improve handling of filters' remote config
first version of the undelete filter
NSS: keep trying to retrieve SSL cert on EAGAIN

We only call the SSL ctx function once when the backend is available, but we
need to avoid stopping here:
[sxi_sslctxfun]: Unable to retrieve certificate for cluster: The operation would have blocked
include errno.h
add missing header file (bb#796)
fix some rev handling and memleak (bb#790)
honour umask with mkdir (bb#792)
curl_multi_timeout might return -1

Docs say that in this case 'You must not wait too long (more than a few seconds perhaps) before you call curl_multi_perform() again'
Merge branch 'master' into gc-merge-2