[develop2] fix require and reference equality

[memsharded]

There is an error in 2.0 when two requires, one with revision and other without revision are used:

• They do not conflict, they are not duplicate
• They can hang the lockfile resolution, due to internal modification of keys in a dict

The tests make it explicit, but the problem is this situation can happen when a profile [tool_requires] collides with a recipe tool_requires, so it is not just about avoiding duplicates in requirements() method, the model must support it.

Alternatives I have tried:

• Keeping the RecipeReference.__eq__ the same, and then adding a new RecipeReference.require_equal() that was used from Require.__eq__ to check if two requires are the same. This approach doesn't need to change the Lockfile.add()
• The proposed one in the PR, in which I change the core RecipeReference.__eq__, that requires changing Lockfile.add(), and now produces an error for a situation that was allowed