5 March 2005: 1.5 Added sha_digest field to global section of config file;
	added support for SHA2 digests (instead of or in addition to SHA1
	digests).
3 September 2004: 1.4a Test for $self->{LINKTARGET_TYPE} being defined
	before using it, for backwards compatibility with old specs.
2 September 2004: 1.4 Test for whether we got file flags results, set to
	"<undefined>" if we didn't.
24 August 2004: Moved file type assignment to separate subroutine.  Added
	new linktarget_type keyword.  Started tracking attributes of link
	targets, except for directory contents.
16 July 2004: 1.3 Fixed bug in check_file command to allow check_file for
	files that don't exist in the file system.  Fixed bug in
	FileAttr::compare that was causing deleted files to sometimes show
	up as added.
14 July 2004: Fixed bug in show_changes subroutine where it was attempting
	to display changed attributes via call to subroutine that requires
	a set as an argument, but supplying a tree.
10 June 2004: 1.2c Fixed bug created by OpenBSD 3.5's move of the
	location of sysctl from /usr/sbin to /sbin.
5 January 2004: 1.2b Fixed bug--stopped calling Digest::SHA1 on dirs
	since it's not supported.
8 April 2003: 1.2a Fixed bug in listing file attributes where special
	characters in file names need to be quoted (now that OpenBSD 3.3
	has a file with a space in its name in the default install).
26 February 2003: 1.2 Fixed bug in file writability check (when file doesn't
	exist), fixed references to directory of spec directories.
25 February 2003: Added better Linux support for file system attributes,
	allow -d paths relative to root_dir, special-cased -d secondary to
	not use PGP or immutable flags and to use a separate changed file.
23 February 2003: Added check for file writability for specifications
	before attempting to write to them.
22 February 2003: Made changes show list of changed attributes for
	each changed path.  Added "new" set code to valid_setlist and
	defined_set in preparation for adding the ability to initialize
	only new sets.  (Need to add code to automatically identify trees
	that don't have specs as members of "new", and to allow initialize
	to work for set new (and only set new) when immutable flags are
	used and securelevel is > 0.  There is a potential problem
	regarding specs for specs.)
22 January 2003: 1.1b Made a change to reset_changed_file.
9 January 2003: 1.1a Fixed bug in changed file support to allow -v support
	for "changes" command to work.
6 January 2003: 1.1 Added file system flags support.  Changed the behavior
	of the "exception:" field for directories (now counts just for the
	directory itself, not any files or directories under it) and added
	"exception-dir:" for the old behavior.  Added -v support to "changes"
	command (it now prints the details that "check" prints).  Allowed "."
	for "exception:" field.
3 March 2001: 1.05 Fixed GPG support and made it the default.
	Host setting will now respect case where no domain name
	is set (pretty much just cosmetic).
2 April 2000: 1.04 Added "ignore" keyword for files that aren't to be
	checked for changes, added "ignored" set in default config file.
28 March 2000: Modified to support chattr +i/-i for Linux immutable
	files.
12 February 2000: 1.03 Added additional documentation to README file.
	Modified Config to make sure that no trees are subtrees of other
	trees. 	Modified to check to make sure that at least one of the
	sets specified with the -s option has members (and warn about
	those that don't).  Added check_file command.  Fixed bug where
	no summary report would be printed if there were no changes,
	only additions or deletions of files.  Added changes command.
11 February 2000:  Modified to correct minor bug in reg exp that validates
	"tree:" fields in conf file.
6 February 2000: 1.02 Modified to correct "new nonexistent added" problem
	which occurred when a file was added after initialization (found
	at time of check) and deleted before update, and to fix problem
	where check summary report wouldn't list sets that had only
	additions and deletions but no changes.
5 February 2000: 1.01 Modified to check existence of files before using
	chflags (added set_immutable_flag subroutine), to record user
	when creating a spec or checking a tree.
30 January 2000:  Version 1.0 created from mtree.pl.
