fix return type of snprintf

Found by Coverity Scan. Compile-tested only.
update LUABackend::setDomainMetadata signature

Found by Coverity Scan. Compile-tested only.
add error checking in exp. recursor webserver

pdns_recursor will now fail to start when it can't bind to the webserver
socket.

Fix for Coverity CID 1029992, 1029999
Remove dead sendData function

Fix for Coverity CID 1029915, which claimed dead code inside the function,
but really, nobody calls it anymore.
Plug leak of include-dir directory pointers

Fix for Coverity CID 1029884.
Don't overflow the sockaddr_un-provided static buffer

sun_path is a buffer with a static length. A too long socket-dir could
overflow it.

Fix for Coverity CID 1029977 & 1029978 (Recursor). While the Auth had
the same problem, there were no Coverity results for it, likely because
of the use of strncpy there.
Provide tighter bounds to HTTP first line parser in Recursor

stringtok over the entire 16k buffer is useless. Also it might make
Coverity shut up.

Tentative fix for Coverity CID 1063848.
Merge pull request #966 from zeha/coverity

Some fixes for Coverity