Canonicalize version before comparing specifiers

[di]

Fixes #282.

[uranusjr]

Thanks for working on this! The fix makes sense to me.

[xavfernandez]

Suggested change

	return hash(self) == hash(other)
	return (self._spec[0], canonicalize_version(self._spec[1])) == (other._spec[0], canonicalize_version(other._spec[1]))

seems cleaner to me than relying on hashes.

[uranusjr]

Personally I like to rely on hash(), since it would be easier to add entries to _spec in the future (if this is ever needed) without the risk of forgetting to update both of them.

[di]

I agree with @uranusjr, I think this is actually cleaner and more clear. And since they're doing essentially the same thing, I don't see any issue with relying on hash here (although maybe I'm missing something).

[xavfernandez]

Well hash() computes a hash meaning you could have a hash collision between two completely different versions.

I'd find something like:

def _canonical_keys(self):
    return self._spec[0], canonicalize_version(self._spec[1])

def __eq__(self, other):
    return self._canonical_keys == other._canonical_keys

def __hash__(self):
    return hash(self._canonical_keys)

cleaner instead of relying on the huge hash space & hash randomization to avoid issues.

[pradyunsg]

Thanks @di for the PR! Thanks @xavfernandez and @uranusjr for the reviews! I think it's perfectly fine to depend on hash. And and, thanks @brettcannon for his review as well!

I got to do the easy-and-fun part. ;)