nhgitset version 4

To update, run "perl DEVEL/nhgitset.pl"

Fixes:
- "nhcommit -a" has been fixed
- NHDT was hardwired in places
- no longer complain about a missing dat directory outside of the
    NetHack source tree
- make update of gitinfo atomic
- Replace some hardwired directory separators with OS-dependent constructs

Backwards Incompatibilities:
- NH_DATESUB's DATE() is now Date() to match the other variables
- MSYS2 requires an additional Perl package - the MSYS2 docs have
    been updated

New Help System:
- git nhhelp
   This command mirrors "git help" for nh* commands.
- See git nhhelp nhsub for general help on substitution variables

New Substitution Variables:
-Brev()
    An aBREViation of $PREFIX-Branch$:$PREFIX-Revision$ - this
    may help get line length under control in file headers.
-Assert(TYPE=VALUE)
    If TYPE does not match VALUE, do not substitute on this line.
    TYPE P checks VALUE against nethack.substprefix
-Project(arg)
    Returns nethack.projectname if there is no arg and an uppercase
    version if arg is uc.

Other New Features:
- Add nethack.projectname
- Documentation updates - see "git nhhelp nhsub"
- On checkout or merge of a branch, check for nhgitset version updates
  and provide an optional message to the user.
- Move NH_DATESUB substitutions here from cron job to keep dates in sync
- PREFIX-* keywords now available in NH_DATESUB templates
- Support use of nhgitset.pl from a different repo; note that update
  checks will be dependent on keeping the original source repo up-to-date
  and in the same location.

DEVEL/hooksdir/NHtext

@@ -3,6 +3,8 @@
 # Copyright (c) 2015 by Kenneth Lorber, Kensington, Maryland
 # NetHack may be freely redistributed.  See license for details.
 
+# Not in use as of v3, but could come back in the future.
+
 # clean/smudge filter for handling substitutions
 use strict;
 
@@ -54,9 +56,9 @@ if($ARGV[0] eq "--clean"){
 	exit 1;
 }
 
-# XXX for now, there isn't any - if we get called, we subst.  No options for now.
+# XX for now, there isn't any - if we get called, we subst.  No options for now.
 # get relevant config info
-#XXX
+#XX
 #git check-attr -a $ARGV[1]
 
 # Process stdin to stdout.
@@ -109,7 +111,7 @@ sub Date {
 	my($val, $mode, $submode) = @_;
 	if($mode eq "c"){
 		if($submode==0){
-			# we add this to make merge easier for now XXX
+			# we add this to make merge easier for now XX
 			my $now = time; # not %s below - may not be portable
 			# YYYY/MM/DD HH:MM:SS
 			$val = "$now " . strftime("%Y/%m/%d %H:%M:%S", gmtime($now));