rewriteutil: add devel warning if precheck is called with contexts
I'm trying to upstream parts from the evolve extension. This check
exists there.
Differential Revision: https://phab.mercurial-scm.org/D10515
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}