* src/ltlast/formula.hh (has_lbt_atomic_props): New method.
* src/ltlast/formula.cc (printprops): Display it.
* src/ltlast/atomic_prop.cc: Update it.
* src/bin/ltlcheck.cc, src/bin/genltl.cc: Use it.
* doc/tl/tl.tex: Menton has_lbt_atomic_props().
* configure.ac: Check for kill and alarm.
* src/bin/ltlcheck.cc: Disable timeout code when kill or alarm are
missing. Recognize the --timeout option, but display a warning.
* lib/gethrxtime.h, lib/xtime.h: Add extern "C".
* src/bin/Makefile.am (ltlcheck_LDADD): Use LIB_GETHRXTIME.
* src/bin/ltlcheck.cc: Use gethrxtime() to record translation time.
* src/misc/formater.hh (printable_value): Add more accessors.
* src/bin/ltlcheck.cc: Use the formater class to factor the %-expansion
loop, and reuse filenames (such as %F, %S, and %L) between executions
on the same formula.