do not link statically to system libs (glibc, threads, etc)

ocamlopt reorders -ccopt so we have to collect all extra libs into
single list and only then wrap it with linker flags -Bstatic .. -Bdynamic
BT: suppress warning for peers6 entry in tracker response
report line and position for syntax errors in config files
EDK: do not dump unknown messages by default
minor typos
Let configure to force using upnp/natpmp at FreeBSD
Allow upnp_stub.c to be compiled on os x