touch: allow divergence with -A even if allowdivergence=no
This is a phase-divergent update to 731b5a89a784.
1f92a6aa40d6 (evolve: add pre-check logic for content-divergence in
rewriteutil.precheck(), 2019-11-04) taught `rewriteutil.precheck()` to
check for divergence. It also set allowdivergence=yes in test-touch.t
to silence the error. However, if one does *not* have that set, it is
no longer possible to allow divergence with `hg touch -A`. This patch
fixes that.