Fixes bug in gpsfake with default port.

The default port number used by gpsfake is (probably incorrectly)
specified as a string rather than an integer.  The shmkey derivation
added in commit 1f20945 expects an integer, causing a failure when
the port is not explicitly specified.  This fix forces an integer
where needed.

TESTED:
Ran "scons build-all check".
Previously failing gpsfake case now works correctly.

gps/fake.py

@@ -549,7 +549,7 @@ def spawn(self, options, port, background=False, prefix=""):
                 % (port, self.control_socket, options))
         # Derive a unique SHM key from the port # to avoid collisions.
         # Use 'Gp' as the prefix to avoid colliding with 'GPSD'.
-        shmkey = '0x4770%.04X' % port
+        shmkey = '0x4770%.04X' % int(port)
         env = {'GPSD_SHM_KEY': shmkey}
         super(DaemonInstance, self).spawn('gpsd', opts, background, prefix,
                                           env)