client: set Content-type of POST requests to text/xml.

Otherwise some RPC-handling frameworks complain.

client/http_curl.cpp

@@ -404,6 +404,8 @@ static int set_cloexec(void*, curl_socket_t fd, curlsocktype purpose) {
 int HTTP_OP::libcurl_exec(
     const char* url, const char* in, const char* out, double offset,
 #ifdef _WIN32
+    // expected size of file we're downloading.
+    // on Win, pre-allocate this file to reduce disk fragmentation
     double size,
 #else
     double,
@@ -559,6 +561,12 @@ int HTTP_OP::libcurl_exec(
         pcurlList = curl_slist_append(pcurlList, buf);
     }
 
+    // if this is a post, set content type (always text/xml)
+    //
+    if (is_post) {
+        pcurlList = curl_slist_append(pcurlList, "Content-type: text/xml");
+    }
+
     // set up an output file for the reply
     //
     if (strlen(outfile)) {