Print directory name on create errors.

Print directory name on create errors.

In create mode, if the database directory already exists, adu prints
an error message of the form

	main: directory exists.

This is a bit sparse, so let's add a log message which prints the
directory name. With the patch applied the output becomes

	open_dir_table: could not create /ebio/maan/tmp/adu-lists/
	main: directory exists