lib/linux_ns: check mkdir() return value

Fail earlier if we can't create the dirs we need.
Reported by Coverity as CID #970969.
core: log when fcntl() fails

Reported by Coverity as CID #970967, #970966.
core: log when sendmsg fails

Reported by Coverity as CID #970962, #970963.
core/cluster: log sendto() error

Reported by Coverity as CID #970958.
new rbtree implementation
Merge pull request #141 from xrmx/coverity5

Check return value of library call Coverity issues
added the sslrouter and various corerouters micro-optimizations
added --sni-dir
fixed --sslrouter-sni
--sslrouter and --sslrouter2 to be more aligned with --https
added --route-referer
fixed realloc() usare in core/io.c as spotted by cppcheck
fixed realloc() usare in core/io.c as spotted by cppcheck [2]
add last_request attribute to subscription node, it will hold the number of requests since last subscription ping
use node->last_requests instead of absolute request counter in (w)lrc
Merge pull request #142 from prymitive/router_delta

add last_request attribute to subscription node, it will hold the number...