pager: rename 'pager.enable' to 'ui.paginate'
This aligns with what we do for color (see 7fec37746417). Pager is a central
enough notion that having the master config in the [ui] section makes senses. It
will helps with consistency, discoverability. It will also help having a simple
and clear example hgrc mentioning pager.
The previous form of the option had never been released in a non-rc version but
we keep it around for convenience. If both are set, 'ui.pager' take priority.
#require docutils gettext
$ $TESTDIR/check-gendoc da
checking for parse errors