MONGOOSE_NO_CGI is implied by both NS_DISABLE_SOCKETPAIR and
MONGOOSE_NO_FILESYSTEM. Thus, so as not to get complaints about
the same define being defined twice, some extra checks are needed.

Conditionally include dirent.h and dlfcn.h

If you do not have a filesystem or do not support dav or
dynamic loading, the corresponding header files need not
be included (some environments might not have them).

Added #define's for deprecated POSIX names

make compile with g++ (fix invalid cast from ‘void*’)

transmit http answer code using http_client