.arcconfig

filemerge: show warning if chosen tool has no binary files capability

While matching patterns in "merge-patterns" configuration, Mercurial
silently assumes that all merge tools have binary files
capability. This implementation comes from 5af5f0f9d724 (or Mercurial
1.0).

At failure of merging binary files with incorrect internal merge tool,
there is no hint about this silent ignorance of binary files
capability.

This patch shows warning message, if chosen internal merge tool has no
binary files capability. This will help users to investigate why a
binary file isn't merged as expected.

{
    "conduit_uri": "https://phab.mercurial-scm.org/api",
    "repository.callsign": "HG",
    "arc.land.onto.default": "@",
    "base": "hg:.^"
}