help: always show command help with -h (issue4240)

Old behavior:
              hg help x    hg x -h    hg help -e x  hg help -c x
config        topic        topic (!)  -             cmd
showconfig    cmd          topic (!)  -             cmd
rebase        cmd          cmd        ext           cmd

New behavior:
              hg help x    hg x -h    hg help -e x  hg help -c x
config        topic        cmd        -             cmd
showconfig    cmd          cmd        -             cmd
rebase        cmd          cmd        ext           cmd

mercurial/dispatch.py

@@ -766,7 +766,7 b' def _dispatch(req):'
     if options['version']:
         return commands.version_(ui)
     if options['help']:
-        return commands.help_(ui, cmd)
+        return commands.help_(ui, cmd, command=True)
     elif not cmd:
         return commands.help_(ui, 'shortlist')
 

tests/test-help.t

@@ -862,6 +862,17 b' test deprecated option is hidden with tr'
   *"hg -v help debugoptDEP"* (glob)
 #endif
 
+Test commands that collide with topics (issue4240)
+
+  $ hg config -hq
+  hg config [-u] [NAME]...
+  
+  show combined config settings from all hgrc files
+  $ hg showconfig -hq
+  hg config [-u] [NAME]...
+  
+  show combined config settings from all hgrc files
+
 Test a help topic
 
   $ hg help revs