This patch creates a hash RFacebook::HTTP_PROXY_OPTIONS which contains the keys:
  :proxy_host, :proxy_port, :proxy_user, and :proxy_pass

It pulls default values from the ENV["http_proxy"] variable, like most unix utilities.  The hash object is
a constant (meaning you can't assign it to be anything other than this hash), but the hash's contents can be modified
in the environment without warning.  This allows you to override the defaul when necessary.

Finally, the patch uses a Net::HTTP::Proxy for creating the http_server in the post_request method.  If the :proxy_host
=> nil, net/http documentation states this will be the same as the previous implementation.