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.
#!/bin/sh
hg init a
echo a > a/a
hg --cwd a ci -Ama
hg clone a c
hg clone a b
echo b >> b/a
hg --cwd b ci -mb
echo % push should push to default when default-push not set
hg --cwd b push | sed 's/pushing to.*/pushing/'
echo % push should push to default-push when set
echo 'default-push = ../c' >> b/.hg/hgrc
hg --cwd b push | sed 's/pushing to.*/pushing/'