[client] spice: protocol updates for performance and agent support

Note: agent support is not complete at this point due to lack of documentation.

client/spice/spice.h

@@ -24,6 +24,7 @@ Place, Suite 330, Boston, MA 02111-1307 USA
 bool spice_connect(const char * host, const unsigned short port, const char * password);
 void spice_disconnect();
 bool spice_process();
+bool spice_agent_process();
 bool spice_ready();
 
 bool spice_key_down      (uint32_t code);