extensions: changed to call extsetup() from extensions.loadall()
previously uisetup() was invoked by extensions.loadall(), but
extsetup() was by _dispatch().
there's no need to split them because we have nothing to do
between uisetup() and extsetup().
this fixes
issue1824 indirectly.
#!/bin/sh
hg init dir
cd dir
echo bleh > bar
hg add bar
hg ci -m 'add bar'
hg cp bar foo
echo >> bar
hg ci -m 'cp bar foo; change bar'
hg debugrename foo
hg debugindex .hg/store/data/bar.i