-J -O: use -O name if no Content-Disposition header comes!

A regression between 7.22.0 and 7.23.0 -- downloading a file with the
flags -O and -J results in the content being written to stdout if and
only if there was no Content-Disposition header in the http response. If
there is a C-D header with a filename attribute, the output is correctly
written.

Reported by: Dave Reisner
Bug: http://curl.haxx.se/mail/archive-2011-11/0030.html

src/tool_operhlp.c

@@ -178,6 +178,24 @@ CURLcode get_url_file_name(char **filename, const char *url)
         return CURLE_OUT_OF_MEMORY;
     }
   }
+
+  /* in case we built debug enabled, we allow an environment variable
+   * named CURL_TESTDIR to prefix the given file name to put it into a
+   * specific directory
+   */
+#ifdef DEBUGBUILD
+  {
+    char *tdir = curlx_getenv("CURL_TESTDIR");
+    if(tdir) {
+      char buffer[512]; /* suitably large */
+      snprintf(buffer, sizeof(buffer), "%s/%s", tdir, *filename);
+      Curl_safefree(*filename);
+      *filename = strdup(buffer); /* clone the buffer */
+      curl_free(tdir);
+    }
+  }
+#endif
+
   return CURLE_OK;
 }