Stop printing at null char option, from Oliver Meyer

	Stop printing at null char option, from Oliver Meyer
	(omeyer@i3.informatik.rwth-aachen.de).
	* valprint.h, valprint.c (stop_print_at_null): New global.
	* valprint.c (_initialize_valprint): New print set subcommand
	"null-stop".
	* c-valprint.c (c_val_print): If stop_print_at_null is on, and
	printing a char	array, adjust the number of chars to print.