revset: do not flip "and" arguments when optimizing Rewrite `flipand(y, x)` to `andsmally(x, y)` so the AST order is unchanged, which could be more friendly to developers. Differential Revision: https://phab.mercurial-scm.org/D579

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.