Improved error message for extensions overriding commands (with test): - Old text "module foo overrides bar" was misread as overriding module bar. - Only print a single warning line per extension instead of one for each command.

*** failed to import extension badext: invalid syntax (badext.py, line 1)
extension 'hgext.gpg' overrides commands: sigs sigcheck sign
hg help [COMMAND]

show help for a command, extension, or list of commands