Yield in connection wait loops to reduce processor use.

Patch by Andrey Vasilkin on mailing list.

libfreerdp/core/activation.c

@@ -290,6 +290,8 @@ BOOL rdp_recv_deactivate_all(rdpRdp* rdp, wStream* s)
 
 		if (freerdp_shall_disconnect(rdp->instance))
 			break;
+
+		SwitchToThread();
 	}
 
 	return TRUE;

libfreerdp/core/connection.c

@@ -336,6 +336,7 @@ BOOL rdp_client_connect(rdpRdp* rdp)
 
 			return FALSE;
 		}
+		SwitchToThread();
 	}
 
 	return TRUE;