Bump version.

On further reflection, last night's seemingly trivial change to
the JSON sending/receiving routines is actually a protocol change,
on some machines, and therefore merits a version number change.

src/version.h

@@ -7,5 +7,5 @@
  * for complete information.
  */
 
-#define IPERF_VERSION "3.0-RC3"
-#define IPERF_VERSION_DATE "01 November 2013"
+#define IPERF_VERSION "3.0-RC4"
+#define IPERF_VERSION_DATE "06 November 2013"