[PATCH 1 of 2 STABLE] help: modernize the example for command registration

[Matt Harbison]

# HG changeset patch
# User Matt Harbison <matt_harbison at yahoo.com>
# Date 1547871184 18000
#      Fri Jan 18 23:13:04 2019 -0500
# Branch stable
# Node ID 9b57d98e8fe910d033575fadeac91be1eae59f6f
# Parent  74525c3e9476db425024f1a8573e66f0473f7a81
help: modernize the example for command registration

diff --git a/mercurial/help/internals/extensions.txt b/mercurial/help/internals/extensions.txt
--- a/mercurial/help/internals/extensions.txt
+++ b/mercurial/help/internals/extensions.txt
@@ -28,11 +28,16 @@ registered to the ``cmdtable`` by ``@com
 
 Example using ``@command`` decorator (requires Mercurial 1.9)::
 
-    from mercurial import cmdutil
     from mercurial.i18n import _
 
     cmdtable = {}
-    command = cmdutil.command(cmdtable)
+    try:
+        from mercurial import registrar
+        command = registrar.command(cmdtable)
+    except (AttributeError, ImportError):
+        # Fallback to hg < 4.3 support
+        from mercurial import cmdutil
+        command = cmdutil.command(cmdtable)
 
     @command('print-parents',
         [('s', 'short', None, _('print short form')),