* include/vaucanson/misc/global_timer.hh: Simplify.  The only
	caller in taf-kit/src/main.cc is already checking for the
	emptyness of the string, and the previous code was using !=
	to compare two char*.
	* taf-kit/src/common.hh (arguments_t::args, arguments_t::alphabet,
	arguments_t::alphabet2): Declare as const char*.
	* taf-kit/src/main.cc (alphabet::name, alphabet::alphabet): Idem.
	* taf-kit/src/pipe.hh, taf-kit/src/pipe.hxx (set_name): Take
	a const argument.