namespaces: add logname member to namespace object Previously, there was no way to change the name used for 'hg log' output. This was inconvenient for extensions that want a template name longer than 12 characters (e.g. remotebookmarks) but a different name for 'hg log'. This patch only adds the member to the object, a future patch will update the 'hg log' code.

namespaces: use named args for namespace api This is just a style change but makes adding new arguments more robust for callers.

namespaces: make the constructor into named args None of the arguments are truly optional but this makes adding future arguments more robust and perhaps optional.