templater: fix string representation of wrapped None flatten() and stringify() skip None, which means wrappedvalue(None).show() must return '' instead of 'None'. This isn't a problem right now, but we'll encounter it once we start using wrapped types extensively.

templater: show slightly better hint on map operation error It was super hard to find where the templater went wrong if a keyword was evaluated to '' or None.

templater: inline unwraphybrid() flatten() is the solo user of this function.

templater: drop hybrid-ness on unwrapvalue() Proxy methods are no longer necessary as list/dict functions go through the wrapped interface.

templater: mark .keytype as a private attribute

templater: abstract ifcontains() over wrapped types This allows us to make .keytype private. There's a minor BC that a hybrid dict/list of keytype=None now strictly checks the type of the needle. For example, {ifcontains(rev, files)} no longer matches a file named "1" at the rev=1. I made this change for consistency with the get(dict, key) function. We can restore the old behavior by making keytype=bytes the default if desired.

templater: inline wraphybridvalue() All wraphybridvalue() calls are now handled in the hybrid class.