Make Julien's review suggestions

README.md:
    Remove references to lcc (hasn't been tried with Mercury for years)
    and the old .NET backend from README.md (likely to cause confusion
    more than anything else).

README.md:
README.IRIX-5:
    Remove the references to IRIX-5 (including the file README.IRIX-5)
    completely.  IRIX is pretty much dead, this documentation is pretty
    much clutter at this point.

README.AIX:
README.HPUX:
    Replacing the contents of README.HPUX and README.AIX to say that
    Mercury (to the best of our knowledge) hasn't been tried with recent
    versions of those OSs.

README.AIX

@@ -1,50 +1,8 @@
------------------------------------------------------------------------------
 
-This file documents what you need to do to get Mercury to work on an
-RS/6000 running AIX using GNU C.
+Mercury hasn't been tested on AIX since 1998.  We are unaware if it works.
+If you have experience with recent versions of Mercury on AIX please let us
+know.
 
-Previous versions of Mercury have worked successfully on AIX,
-but Rodney Brown <rodneybrown@pmsc.com> reported some problems
-with a recent version.  We believe that we have fixed these problems,
-but we do not have a machine running AIX to test it on, so we do 
-not know if the current version will build correctly out-of-the-box.
+Contact information:
+http://www.mercurylang.org/contact.html
 
-If there are any problems remaining, we would be happy to assist
-in resolving them.
-
------------------------------------------------------------------------------
-
-1.  Put the following line in the file Mmake.params:
-
-	EXTRA_CFLAGS=-mminimal-toc
-
-    This works around a fixed limit on the size of the TOC (Table of Contents)
-    in the RS/6000 object file format.
-
-2.  Follow the instructions in the INSTALL file.
-
-The last version of Mercury which was known to work on AIX was
-Mercury 0.6 -- actually a version just prior to 0.6, namely
-the 30Apr1996 development snapshot (the sources for this version
-are still available from our CVS repository).
-That version was verified to work on AIX 4.1.3 using GNU C 2.7.2.
-For that version, following the steps above would result in
-an error message from the assembler, so the following additional
-step was needed.
-
-3. Change directory to the `compiler' directory, and run the command
-
-	sh ../scripts/rs6000_hack
-
-   Then continue following the instructions in the INSTALL file.
-
-   This works around a fixed limit of 32k on the size of relative jumps
-   in the RS/6000 object file format.
-
-It is possible that something similar to this will still be needed,
-but the rs6000_hack script no longer works as is, so a little more
-hacking will be needed if that is the case. 
-(We'd be happy to offer assistance with this task.  Indeed, we'd do it
-ourselves, but we don't have an AIX machine -- donations happily accepted ;-)
-
------------------------------------------------------------------------------

README.HPUX

@@ -1,4 +1,7 @@
-Mercury installs fine out-of-the-box on HPUX 10.20, according to
-Rodney Brown <rodneybrown@pmsc.com>.  However, you may need to
-use an egcs release (see <http://egcs.cygnus.com>) instead of
-standard gcc.  Rodney Brown used egcs 1.1.
+
+Mercury hasn't been tested on HPUX since 1998.  We are unaware if it works.
+If you have experience with recent versions of Mercury on AIX please let us
+know.
+
+Contact information:
+http://www.mercurylang.org/contact.html

README.IRIX-5

@@ -1,20 +0,0 @@
-
-We have not been able to test the Irix 5 port since March 2000,
-due to lack of access to an Irix 5 machine.
-
-On Irix 5, it is not possible to use both gcc's non-local gotos and
-position-independent code (which is required for shared libraries).
-The Mercury auto-configuration script should resolve this problem
-by disabling the use of gcc's non-local gotos (e.g. the `asm_fast.gc'
-grade).
-
-Use of non-local gotos on Irix 5 was supported in previous releases of
-Mercury, but now we recommend using the hlc.gc grade instead.
-
-If you install from the source distribution, the initial version of the
-compiler will use grade reg.gc.  You can get a faster compiler by
-adding the directory for the installed mmc to your PATH and then
-reinstalling from the source distribution.  The second time around,
-the configure script will detect that a working mmc is in your PATH
-and will build the compiler in grade hlc.gc rather than grade reg.gc.
-

README.md

@@ -26,7 +26,6 @@ Specific information is contained in individual README files:
     This backend works well with GCC but also works with:
 
       * [Clang](README.clang)
-      * [lcc](README.lcc)
 
   * High-level backend targets
 
@@ -35,10 +34,6 @@ Specific information is contained in individual README files:
       * [Erlang](README.Erlang)
       * [Java](README.Java)
 
-  * Experimental / Obsolete backends
-
-      * [.Net IL](README.DotNet)
-
   * Platforms
 
       * [Linux](README.Linux)
@@ -49,7 +44,6 @@ Specific information is contained in individual README files:
       * [FreeBSD](README.FreeBSD)
       * [AIX](README.AIX)
       * [HP-UX](README.HPUX)
-      * [IRIX-5](README.IRIX-5)
       * [Solaris](README.Solaris)
       * [Windows](README.MS-Windows)
         ([Visual C](README.MS-VisualC),