DWDS/Dialing Concordance Code

* added UNIX socket support for CCurl and TxCab classes
- uses CURLOPT_UNIX_SOCKET_PATH (libcurl >= v7.40.0) for now
+ TODO: get emulation working in libcurl < v7.40.0
- supported URL formats:
+ "http:/path/to/unix/socket//uri/path" (perl LWP::Protocol::http::SocketUnixAlt style)
+ "unix:/path/to/unix/socket|http:///uri/path" (apache mod_proxy style)
+ "http+unix:/path/to/unix/socket//uri/path" (native http+unix scheme, //-separated)
+ "http+unix:/path/to/unix/socket|/uri/path" (native http+unix scheme, |-separated)