setup: hgbuildmo inherits from Command

hgbuildmo does not need anything provided by the build class.

setup.py

@@ -192,7 +192,7 b' class hgbuild(build):'
     sub_commands = [('build_mo', None),
                    ] + build.sub_commands
 
-class hgbuildmo(build):
+class hgbuildmo(Command):
 
     description = "build translations (.mo files)"
 
@@ -222,6 +222,12 b' class hgbuildmo(build):'
             self.mkpath(join('mercurial', modir))
             self.make_file([pofile], mobuildfile, spawn, (cmd,))
 
+    def initialize_options(self):
+        pass
+
+    def finalize_options(self):
+        pass
+
 
 class hgdist(Distribution):
     pure = 0