Add option to cross-connect calls; Calls between mobiles are now possible

Use -x to enable call cross-connect. No MNCC socket, no call device must
be specified!

Be sure to have at least one control channel and two voice channels.
Alternatively you can use one combined control/voice channel and one
voice channel.

src/common/Makefile.am

@@ -28,6 +28,7 @@ libmobile_a_SOURCES = \
 	call.c \
 	testton.c \
 	mncc_console.c \
+	mncc_cross.c \
 	mncc_sock.c \
 	hagelbarger.c \
 	display_status.c \