util: set correct stack level on deprecation warnings

Without this patch, you'll get something like this:

  <path>/mercurial/util.py:3784: DeprecationWarning: 'util.hgexecutable'
      is deprecated, use 'utils.procutil.hgexecutable'

(but on one line)

Differential Revision: https://phab.mercurial-scm.org/D3331

mercurial/util.py

@@ -3781,7 +3781,7 b' def _deprecatedfunc(func, version, modna'
         fn = pycompat.sysbytes(func.__name__)
         mn = modname or pycompat.sysbytes(func.__module__)[len('mercurial.'):]
         msg = "'util.%s' is deprecated, use '%s.%s'" % (fn, mn, fn)
-        nouideprecwarn(msg, version)
+        nouideprecwarn(msg, version, stacklevel=2)
         return func(*args, **kwargs)
     wrapped.__name__ = func.__name__
     return wrapped