detail on my changeset

[bjin]

feel free to comment on my patch

• proxy auth (basic/digest scheme) for http-connect/http-relay
  It's the reason I forked this project. unlike socks5 or http basic auth, http digest auth is a challenge-response type. After receiving an 403 status response containing an auth challenge, we calculate a new response and reconnect to proxy server.
  To be effective, I add a http_auth structure for each http proxy instance(not client), so in most case, only first client connection require two relay connections for each instance.
  I added base64.c for basic scheme and md5.c for digest scheme, along with a rfc document.
  there is a FIXME in redsocks.c:redsocks_onenter(), I can't calloc exact memory for an instance before parsing the config file.
• some code cleanup, add support for clang, clean warnings
  the only changes I'm not quite sure is that: clang didn't support variable-length array in an union, so I reimplement two blocks of code in socks4/5.c using calloc.
• add -p command line option, which is useful for daemon scripts

[darkk]

free(NULL) is legal almost everywhere (embedded?), the only reason to have free_null macro is to nullify pointer after freeing.

[darkk]

Thank you! I've merged your changes - I've not deeply reviewed http-related code as I left it in half-broken state years ago, so I assume that at least it works for you now. :-)