Fix tests for object registry.
Avoid download_get signal.
Add a scope parameter to objreg functions.
Use object registry for keyparsers.
Add scope argument to cmdutils.register/commands.
Add a registry argument to objreg.register.
Add a tab-scope object registry.
Use object registry for hintmanager.
Add 'meta' scope to objreg.
Register tab registry in meta registry.
Fix lint