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
cat > $HGRCPATH <<EOF
[extensions]
alias=
[alias]
myinit = init
cleanstatus = status -c
unknown = bargle
ambiguous = s
recursive = recursive
EOF
echo '% basic'
hg myinit alias
echo '% unknown'
hg unknown
echo '% ambiguous'
hg ambiguous
echo '% recursive'
hg recursive
cd alias
echo foo > foo
hg ci -Amfoo
echo '% with opts'
hg cleanst