.arcconfig

procutil: don't allow the main 'hg' script to be treated as the Windows exe

Previously, there were a handful of errors like this:

     $ hg prefetch --repack
     (running background incremental repack)
  +  abort: %1 is not a valid Win32 application
  +  [255]

CreateProcess() doesn't append .exe when `lpApplicationName` contains a path,
and a python script isn't directly executable.

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