Print help menu when no subcommands applied

Made subparsers not required in the main parser, but if no commands are parsed,
then the parser prints its help.  When a command is present, the normal
functionality preserved.

Removed the single unittest that checks for this exact behavior.

pubs/pubs_cmd.py

@@ -69,7 +69,7 @@ def execute(raw_args=sys.argv):
                                          prog="pubs", add_help=True)
         parser.add_argument('--version', action='version', version=__version__)
         subparsers = parser.add_subparsers(title="valid commands", dest="command")
-        subparsers.required = True
+        #subparsers.required = True
 
         # Populate the parser with core commands
         for cmd_name, cmd_mod in CORE_CMDS.items():
@@ -85,8 +85,11 @@ def execute(raw_args=sys.argv):
         autocomplete(parser)
         # Parse and run appropriate command
         args = parser.parse_args(remaining_args)
-        args.prog = "pubs"  # FIXME?
-        args.func(conf, args)
+        if not args.command:
+            parser.print_help()
+        else:
+            args.prog = "pubs"  # FIXME?
+            args.func(conf, args)
 
     except Exception as e:
         if not uis.get_ui().handle_exception(e):

tests/test_usecase.py

@@ -187,13 +187,6 @@ class URLContentTestCase(DataCommandTestCase):
 
 # Actual tests
 
-class TestAlone(CommandTestCase):
-
-    def test_alone_misses_command(self):
-        with self.assertRaises(FakeSystemExit):
-            self.execute_cmds(['pubs'])
-
-
 class TestInit(CommandTestCase):
 
     def test_init(self):