help: pass sub-topic into help query functions

While we will likely only use this variable in helptopic(), all these
functions are called with the same arguments, so we have to be
consistent.

mercurial/help.py

@@ -263,7 +263,7 b' def help_(ui, name, unknowncmd=False, fu'
 
     import commands # avoid cycle
 
-    def helpcmd(name):
+    def helpcmd(name, subtopic=None):
         try:
             aliases, entry = cmdutil.findcmd(name, commands.table,
                                              strict=unknowncmd)
@@ -432,7 +432,7 b' def help_(ui, name, unknowncmd=False, fu'
                            % (name and " " + name or ""))
         return rst
 
-    def helptopic(name):
+    def helptopic(name, subtopic=None):
         for names, header, doc in helptable:
             if name in names:
                 break
@@ -460,7 +460,7 b' def help_(ui, name, unknowncmd=False, fu'
             pass
         return rst
 
-    def helpext(name):
+    def helpext(name, subtopic=None):
         try:
             mod = extensions.find(name)
             doc = gettext(mod.__doc__) or _('no help text available')
@@ -496,7 +496,7 b' def help_(ui, name, unknowncmd=False, fu'
                        ' extensions)\n'))
         return rst
 
-    def helpextcmd(name):
+    def helpextcmd(name, subtopic=None):
         cmd, ext, mod = extensions.disabledcmd(ui, name,
                                                ui.configbool('ui', 'strict'))
         doc = gettext(mod.__doc__).splitlines()[0]
@@ -545,7 +545,7 b' def help_(ui, name, unknowncmd=False, fu'
             queries = (helptopic, helpcmd, helpext, helpextcmd)
         for f in queries:
             try:
-                rst = f(name)
+                rst = f(name, subtopic)
                 break
             except error.UnknownCommand:
                 pass