exchange: hit opargs with pycompat.strkwargs before **-ing it Fixes Python 3 problems.

revlog: update signature of dummy addgroup() in bundlerepo and unionrepo Per c8b6ed51386b, 2f5c45fe3a3b and 00e3f909907f.

py3: use 'surrogatepass' error handler to process U+DCxx transparently It's disallowed by default on Python 3. https://docs.python.org/3/library/codecs.html#error-handlers

py3: don't pass bytes to array.array()

py3: wrap bytes in encoding.from/toutf8b() with bytestr

py3: iterate bytes as a byte string in store.lowerencode()

py3: use bytechr() in store._buildlowerencodefun()

store: give name to lowerencode function lambda function isn't easy to track in traceback.