OrdredDict is in the standard library for all supported Python versions
(2.7 and 3.5+) and has improvements over the ActiveState recipe version
of OrderedDict we have been using. Switch to importing from collections
instead of getting it from SCons.Util (tests already did this).
At the same time, reorganize the Util.py imports - import Iterable
from collections.abc if possible (it is deprecated to import
it from collections, will stop working in 3.8); try getting the
User{Dict,List,String} from collections if possible - that is, try the
3.x way first.
Signed-off-by: Mats Wichmann <mats@linux.com>
https://github.com/SCons/scons/commit/3fa7141ec7b39
