- Makefile (DIRS): added atrf-xtal
- atrf-xtal/Makefile: build atrf-xtal for the Ben or do nothing elsewhere
- atrf-xtal/atrf-xtal.h, atrf-xtal/atrf-xtal.c: diagnostic utility to
determine the transceiver's crystal frequency
- atrf-xtal/atben.c: dirty low-level driver for ATBEN