Added XHOST.

Resolves #320

Source from MC: ALAN; XHOST 36.

doc/info/xhost.5

@@ -0,0 +1,87 @@
+-*- Text -*-
+
+File: XHOST	Node: Top	Up: (DIR)
+
+After 31 March 1987 the NIC will no longer allow alternate host names
+(nicknames) to appear in the Official Host Table or domain name servers.
+Unfortunately there are many mailing list files around that contain entries
+using these soon-to-be-obsolete hostnames.  XHOST is a tool for assisting
+in the conversion of such mailing list files to use only "approved" host
+names.
+
+XHOST has two parts.  There is an :XHOST program that reads a mailing list
+file and writes an "XHOST" file in which all nicknames have been flagged,
+and an XHOST Emacs library that contains an Emacs command for performing a
+query-replace-style scan of an XHOST file.
+
+:XHOST takes the name of a mailing list file as an argument, and writes a
+file whose second name is XHOST.  For example:
+
+  :XHOST GUBBLE PEOPLE
+
+will read the file GUBBLE PEOPLE from your working directory and write a
+file there named GUBBLE XHOST.
+
+The format of an XHOST file is fairly simple.  Each nickname that :XHOST
+thinks it has found will be immediately followed by rubout ("¢, ASCII
+code 177).  Following the rubout is the hostname that XHOST recommends as a
+replacement.  
+
+The replacement will start with an atsign ("@") if the original hostname
+did not.  This will turn an entry like "(RPG SU-AI)" into the preferred form
+"(RPG @SAIL.STANFORD.EDU)", which will result in better host name error
+reporting from the mailer.
+
+:XHOST does -not- really understand the format of mailing list files.  It
+understands how to parse comments, but it does not understand the parenthesis
+structure.  Thus occasionally it will offer to turn a user name into a
+hostname.  For example it might offer:
+
+  HENRYÀHENRY.ECE.CMU.EDU
+
+Watching out for things like this will keep you on your toes.  (XHOST has a
+table of known absurd replacements such as "DanG" => "NYU-DANGER.ARPA".
+The maintainer will accept nominations for additions.)
+
+Loading the XHOST Emacs library defines a single Emacs command:
+M-X Canonicalize Hosts.  This command scans through an XHOST file searching
+for the hostnames flagged by :XHOST.  For each one that it finds, you can
+accept or decline the proposed replacement.  M-X Canonicalize Hosts behaves
+very much like M-X Query Replace.  The complete list of commands it accepts
+are:
+
+	Space	- Replace old host name with new.
+	Rubout	- Leave old host name as it is.
+	N	- Nothing.  Leave both host names in buffer.
+	U	- Undo last change.
+	C-L	- Redisplay.
+	C-R	- Enter recursive ^R mode.
+	Q	- Quits.
+	?	- Self documentation.
+
+As an additional feature, if M-X Canonicalize Hosts does not find any
+flagged names in the currently selected buffer, it assumes that you
+probably need to run :XHOST first.  It offers to write out the current
+buffer if necessary, and then sends a command to DDT to run :XHOST over
+that file and then return to Emacs.  When :XHOST is complete, the XHOST
+file is read back into the current buffer and M-X Canonicalize Hosts starts
+its normal scan.
+
+Thus the easiest way to update the mailing list file GUBBLE PEOPLE is to
+
+  1.  read GUBBLE PEOPLE into an Emacs buffer
+  2.  do M-X Load Library$XHOST if you haven't already in this Emacs
+  3.  do M-X Canonicalize Hosts
+  4.  answer "Y" when it offers to run :XHOST,
+  5.  get a cup of tea while :XHOST runs, it's not instantaneous
+  6.  decide what to do about each host one-by-one as M-X Canonicalize
+      Hosts shows them to you
+  7.  write the resulting file back out over the old GUBBLE PEOPLE.
+
+There will still be a GUBBLE XHOST file sitting around when you are
+finished.  If you are 100% certain that what you just did was correct, then
+you can just delete it.  If you decide that you screwed up, you can always
+recover by reading in GUBBLE XHOST, and running M-X Canonicalize Hosts
+again.
+
+Bugs, suggestions, etc. to Alan@AI.