xstrncpy saga

xstrncpy saga

	* src/fileio.c (file_name_as_directory): Use xstrncpy and change
	prototype to take in buffer length.

	* src/fileio.c (directory_file_name): Ditto.

	* src/fileio.c (Ffile_name_as_directory): properly call
	file_name_as_directory with buffer length.
	* src/fileio.c (Fdirectory_file_name): ditto.

	* src/fileio.c (Fexpand_file_name): Use xstrncat instead of strcat.

	* src/fileio.c (Fdirectory_file_name): properly call
	directory_file_name with buffer length.

	* src/fileio.c (Fsubstitute_in_file_name): use xstrncpy instead of
	strcpy keeping track of buffer availability.

Signed-off-by: Nelson Ferreira <nelson.ferreira@ieee.org>