Fixes cpp-netlib#35

Making calls to client.post and client.put smarter with the provided request objects.

Author: deanberris

boost/network/protocol/http/client/facade.hpp

@@ -41,8 +41,9 @@ namespace boost { namespace network { namespace http {
 
         response const post (request request_, string_type const & content_type, string_type const & body_) {
             request_ << ::boost::network::body(body_)
-                << header("Content-Type", content_type)
                 << header("Content-Length", boost::lexical_cast<string_type>(body_.size()));
+            if (!boost::empty(headers(request_)["Content-Type"]))
+                request_ << header("Content-Type", content_type);
             return post(request_);
         }
 
@@ -60,8 +61,9 @@ namespace boost { namespace network { namespace http {
 
         response const put (request request_, string_type const & content_type, string_type const & body_) {
             request_ << ::boost::network::body(body_)
-                << header("Content-Type", content_type)
                 << header("Content-Length", boost::lexical_cast<string_type>(body_.size()));
+            if (!boost::empty(headers(request_)["Content-Type"]))
+                request_ << header("Content-Type", content_type);
             return put(request_);
         }