perf: define command annotation locally for Mercurial earlier than 3.1

Before this patch, using cmdutil.command() for "@command" annotation
prevents perf.py from being loaded by Mercurial earlier than 1.9 (or
2daa5179e73f), because cmdutil.command() isn't available in such
Mercurial, even though there are some code paths for Mercurial earlier
than 1.9.

For example, setting "_prereadsize" attribute in perfindex() and
perfnodelookup() is effective only with hg earlier than 1.8 (or
61c9bc3da402).

In addition to it, "norepo" option of command annotation has been
available since 3.1 (or 75a96326cecb), and this is another blocker for
loading perf.py with earlier Mercurial.

  ============ ============ ======
               command of
  hg version   cmdutil      norepo
  ============ ============ ======
  3.1 or later      o         o
  1.9 or later      o         x
  earlier           x         x
  ============ ============ ======

This patch defines "command()" for annotation locally as below:

  - define wrapper of existing cmdutil.command(), if cmdutil.command()
    doesn't support "norepo"
    (for Mercurial earlier than 3.1)

  - define full command() locally with minimum function, if
    cmdutil.command() isn't available at runtime
    (for Mercurial earlier than 1.9)

This patch also defines parsealiases() locally without examining
whether it is available or not, because it is small enough to define
locally.

contrib/perf.py

@@ -67,7 +67,39 revlogopts = getattr(commands, "debugrev
         ])
 
 cmdtable = {}
+
+# for "historical portability":
+# define parsealiases locally, because cmdutil.parsealiases has been
+# available since 1.5 (or 6252852b4332)
+def parsealiases(cmd):
+    return cmd.lstrip("^").split("|")
+
+if safehasattr(cmdutil, 'command'):
+    import inspect
 command = cmdutil.command(cmdtable)
+    if 'norepo' not in inspect.getargspec(command)[0]:
+        # for "historical portability":
+        # wrap original cmdutil.command, because "norepo" option has
+        # been available since 3.1 (or 75a96326cecb)
+        _command = command
+        def command(name, options=(), synopsis=None, norepo=False):
+            if norepo:
+                commands.norepo += ' %s' % ' '.join(parsealiases(name))
+            return _command(name, list(options), synopsis)
+else:
+    # for "historical portability":
+    # define "@command" annotation locally, because cmdutil.command
+    # has been available since 1.9 (or 2daa5179e73f)
+    def command(name, options=(), synopsis=None, norepo=False):
+        def decorator(func):
+            if synopsis:
+                cmdtable[name] = func, list(options), synopsis
+            else:
+                cmdtable[name] = func, list(options)
+            if norepo:
+                commands.norepo += ' %s' % ' '.join(parsealiases(name))
+            return func
+        return decorator
 
 def getlen(ui):
     if ui.configbool("perf", "stub"):