Added CURLOPT_LOCALPORT and CURLOPT_LOCALPORTRANGE to libcurl. Set with the

curl tool with --local-port. Plain and simply set the range of ports to bind
the local end of connections to. Implemented on to popular demand.

Not extensively tested. Please let me know how it works.

lib/urldata.h

@@ -970,7 +970,10 @@ struct UserDefined {
                                of strlen(), and then the data *may* be binary
                                (contain zero bytes) */
   char *ftpport;     /* port to send with the FTP PORT command */
-  char *device;      /* network interface to use */
+  char *device;      /* local network interface/address to use */
+  unsigned short localport; /* local port number to bind to */
+  int localportrange; /* number of additional port numbers to test in case the
+                         'localport' one can't be bind()ed */
   curl_write_callback fwrite;        /* function that stores the output */
   curl_write_callback fwrite_header; /* function that stores headers */
   curl_read_callback fread;          /* function that reads the input */