Add transparent dash support to commands.

subcommand.py

Index: subcommand.py
diff --git a/subcommand.py b/subcommand.py
index 6afe3dcda1d31b458174f97c491dcf4ab0fb68d7..0b0fa6e30206d9495c004420aede869b8922f685 100644
--- a/subcommand.py
+++ b/subcommand.py
@@ -119,6 +119,9 @@ class CommandDispatcher(object):
     It automatically tries to guess the intended command by handling typos or
     incomplete names.
     """
+    # Implicitly replace foo-bar to foo_bar since foo-bar is not a valid python
+    # symbol but it's faster to type.
+    name = name.replace('-', '_')
     commands = self.enumerate_commands()
     if name in commands:
       return commands[name]