revset: make match function follow given subset if specified (API)
This should be sensible default since mfunc(subset) is roughly equivalent
to 'subset & mfunc'. The order argument is still there so we can specify
'anyorder' if the order doesn't really matter.
pager.pager=p0 # $TESTTMP/sysrc:4
ui.editor=e1 # $TESTTMP/userrc:2
pager.pager=p2 # $PAGER
ui.editor=e1 # $TESTTMP/userrc:2