Move cmdtable and reposetup handling out of extensions.py A new function (extensions.extensions) allows the code that is interested in those attributes to handle them directly. This allows some cleanups of extensions.py. Notably, we can remove the extensions.commandtable hack. It also makes it easier to add standard extension attributes, like a "hgwebsetup" function or a "helptable" dict that augments the data in help.py, etc.

Is there an error message when trying to diff non-existing files?
found: No such file or directory
not: No such file or directory
Is there an error message when trying to add non-existing files?
found: No such file or directory
not: No such file or directory