[PATCH 3 of 3 evolve-ext] errors: add missing imports of mercurial.error

[Yuya Nishihara]

On Fri, 28 Oct 2016 17:56:13 -0700, Martin von Zweigbergk via Mercurial-devel wrote:
> On Fri, Oct 28, 2016 at 5:52 PM, Pierre-Yves David
> >> diff -r 961b53077cab -r 406fdf786dfa hgext/obsolete.py
> >> --- a/hgext/obsolete.py Fri Oct 28 17:15:57 2016 -0700
> >> +++ b/hgext/obsolete.py Fri Oct 28 17:25:06 2016 -0700
> >> @@ -13,7 +13,7 @@
> >>  were such user.
> >>  """
> >>
> >> -from mercurial import util
> >> +from mercurial import error
> >>
> >>  try:
> >>      from mercurial import obsolete
> >> @@ -24,9 +24,9 @@
> >>  import json
> >>
> >>  from mercurial import cmdutil
> >> -from mercurial import error

This try-except appears to be a dead code. It would never raise ImportError
because of demandimport, and the obsolete module isn't used at all.