setup: tweak error message for Python 3
We now have beta support for Python 3. In my opinion, it isn't
yet stable enough to allow `pip install Mercurial` to work with
Python 3 out of the box: we don't want people accidentally using
Mercurial with Python 3 just yet.
But I do think we should be more friendly about informing people
of their options.
This commit tweaks the error message that users see when running
setup.py with Python 3. We instruct them about the current level
of Python 3 support, point them at the wiki for more info, and
give them instructions on how to bypass the check.
As part of this, I also changed which version value is printed,
as we were printing a named tuple before.
{
// Enforcing
"eqeqeq" : true, // true: Require triple equals (===) for comparison
"forin" : true, // true: Require filtering for..in loops with obj.hasOwnProperty()
"freeze" : true, // true: prohibits overwriting prototypes of native objects such as Array, Date etc.
"nonbsp" : true, // true: Prohibit "non-breaking whitespace" characters.
"undef" : true, // true: Require all non-global variables to be declared (prevents global leaks)
// Environments
"browser" : true // Web Browser (window, document, etc)
}