[m-rev.] for review: comment out documentation of experimental GC methods

[Julien Fischer]

For review by anyone.

(The experimental GC methods were commented out in the users' guide
some time ago.)
------------------------

Comment out documentation of experimental GC methods.

compiler/options.m:
    As above.

.INSTALL.in:
    Document --enable-nogc-grades rather than --disable-nogc-grades.
    (The configure script was swapped over a long time ago.)
    Explain why these grades are not enabled by default.

Julien.

diff --git a/.INSTALL.in b/.INSTALL.in
index 2711d58..f6d2b76 100755
--- a/.INSTALL.in
+++ b/.INSTALL.in
@@ -140,8 +140,10 @@ make install
 #          grades corresponding to the `--debug' and `--high-level-code'
 #          options).
 #
-#          The option --disable-nogc-grades prevents the installation
-#          of grades without garbage collection.
+#          The option --enable-nogc-grades causes the installation
+#          of grades without garbage collection.  These are not generally
+#          useful as most programs compiled using them will quickly run out
+#          of memory.
 #
 #          The option --disable-prof-grades prevents the installation
 #          of grades that support profiling.
diff --git a/compiler/options.m b/compiler/options.m
index b5f9a7b..442b9a1 100644
--- a/compiler/options.m
+++ b/compiler/options.m
@@ -5677,19 +5677,23 @@ options_help_compilation_model(Stream, !IO) :-
     io.write_string(Stream,
         "\n      Miscellaneous optional features\n", !IO),
     io.write_prefixed_lines(Stream, "\t", [
-        "--gc {none, boehm, hgc, accurate, automatic}",
-        "--garbage-collection {none, boehm, hgc, accurate, automatic}",
+        % Documentation for the "accurate" and "hgc" GC methods is
+        % commented out as those methods are still experimental
+        %"--gc {none, boehm, hgc, accurate, automatic}",
+        %"--garbage-collection {none, boehm, hgc, accurate, automatic}",
+        "--gc {none, boehm, automatic}",
+        "--garbage-collection {none, boehm, automatic}",
         "\t\t\t\t(`java' and `csharp' grades",
         "\t\t\t\t\t use `--gc automatic',",
         "\t\t\t\t`.gc' grades use `--gc boehm',",
-        "\t\t\t\t`.hgc' grades use `--gc hgc',",
+        %"\t\t\t\t`.hgc' grades use `--gc hgc',",
         "\t\t\t\tother grades use `--gc none'.)",
         "\tSpecify which method of garbage collection to use",
         "\t(default: boehm).",
         "\t`boehm' is Hans Boehm et al's conservative collector.",
-        "\t`hgc' is our own conservative collector;",
-        "\t`accurate' is our own type-accurate copying GC;",
-        "\tit requires `--high-level-code'.",
+        %"\t`hgc' is our own conservative collector;",
+        %"\t`accurate' is our own type-accurate copying GC;",
+        %"\tit requires `--high-level-code'.",
         "\t`automatic' means the target language provides it.",
         "\tThis is the case for the C# and Java back-ends,",
         "\twhich always use the garbage collector of the underlying",