If local repository is missing, make error message clearer.

Faheem Mitha suggested finding a better error message.
The nice error message is taken from cogito.

mercurial/commands.py

@@ -2458,7 +2458,8 b' def serve(ui, repo, **opts):'
 
     if opts["stdio"]:
         if repo is None:
-            raise hg.RepoError(_('no repo found'))
+            raise hg.RepoError(_("There is no Mercurial repository here"
+                                 " (.hg not found)"))
         s = sshserver.sshserver(ui, repo)
         s.serve_forever()
 
@@ -2469,7 +2470,8 b' def serve(ui, repo, **opts):'
             ui.setconfig("web", o, opts[o])
 
     if repo is None and not ui.config("web", "webdir_conf"):
-        raise hg.RepoError(_('no repo found'))
+        raise hg.RepoError(_("There is no Mercurial repository here"
+                             " (.hg not found)"))
 
     if opts['daemon'] and not opts['daemon_pipefds']:
         rfd, wfd = os.pipe()

mercurial/hgweb/server.py

@@ -207,7 +207,8 b' def create_server(ui, repo):'
                 hgwebobj = self.repoviewmaker(repo.__class__(repo.ui,
                                                              repo.origroot))
             else:
-                raise hg.RepoError(_('no repo found'))
+                raise hg.RepoError(_("There is no Mercurial repository here"
+                                     " (.hg not found)"))
             return hgwebobj
 
     class IPv6HTTPServer(MercurialHTTPServer):

mercurial/localrepo.py

@@ -27,7 +27,8 b' class localrepository(repo.repository):'
                 oldp = p
                 p = os.path.dirname(p)
                 if p == oldp:
-                    raise repo.RepoError(_("no repo found"))
+                    raise repo.RepoError(_("There is no Mercurial repository"
+                                           " here (.hg not found)"))
             path = p
         self.path = os.path.join(path, ".hg")