Add simplistic telnet control interface

This might turn into a complete wire protocol with special
client software. For now it will be a simple client interface
that you can use with telnet to do certain things.

This is using flex to implement the parsing. Implementation
and more commands will follow.
diff --git a/src/Makefile.am b/src/Makefile.am
index 62afff2..b0e29ee 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -5,5 +5,5 @@
 
 bsc_hack_SOURCES = bsc_hack.c misdn.c abis_rsl.c abis_nm.c gsm_04_08.c gsm_data.c \
 		gsm_subscriber.c msgb.c select.c chan_alloc.c timer.c debug.c db.c \
-		gsm_04_11.c
+		gsm_04_11.c telnet_interface.c telnet_parser.l
 bsc_hack_LDADD = -ldl -ldbi