setup: ignore message about disabling 3rd party extensions because of version

I started getting into a bind recently when switching between py2 and py3
because switching requires a `make clean`, which kills __version__.py.  But then
when running `make local`, it picks up the local hg.exe (MSYS seems to prefix
$PATH with '.'), which doesn't know its version.  That causes it to emit a
warning about needing at least 4.3 to load evolve, which caused setup.py to fail
saying there is no working hg executable to figure out the version.  If we can
ignore general extension import failures, we should be able to ignore this too.

setup.py

@@ -262,7 +262,9 b' def filterhgerr(err):'
                and not e.startswith(b'warning: Not importing')
                and not e.startswith(b'obsolete feature not enabled')
                and not e.startswith(b'*** failed to import extension')
-               and not e.startswith(b'devel-warn:'))]
+               and not e.startswith(b'devel-warn:')
+               and not (e.startswith(b'(third party extension')
+                        and e.endswith(b'or newer of Mercurial; disabling)')))]
     return b'\n'.join(b'  ' + e for e in err)
 
 def findhg():