help: show advanced, experimental and deprecated extensions with --verbose

I noticed that phabricator and absorb weren't showing up, no matter what.
There's a related problem where commands for these extensions *do* show up
without --verbose.  I'm not sure what the point of hiding the extensions, but
not the commands is.

mercurial/help.py

@@ -616,7 +616,8 b' def help_(ui, commands, name, unknowncmd'
         ex = opts.get
         anyopts = (ex(r'keyword') or not (ex(r'command') or ex(r'extension')))
         if not name and anyopts:
-            exts = listexts(_('enabled extensions:'), extensions.enabled())
+            exts = listexts(_('enabled extensions:'), extensions.enabled(),
+                            showdeprecated=ui.verbose)
             if exts:
                 rst.append('\n')
                 rst.extend(exts)