py3: convert exceptions to bytes using pycompat.bytestr()

py3: use "%d" for formatting integers

py3: avoid "%s" for formatting None

py3: use "%f" for formatting floating point number

py3: fix progress() functions to not use "%s" with int Python3 doesn't support "%s" with int arguments (and not with None arguments either, which this code was also using).

py3: make random topic name generation consistent across py2/py3 random.choice() (and others based on random.randint()) changed between py2 and py3 without a way to get the py2 behavior. However, random.random() did not change, so we can re-implement random.choice() based on that.

py3: convert str to bytes before passing to core exception

py3: convert opts keys to bytes before passing to core APIs

evolve: further clarify when update is performed

py3: avoid comparing int and None

py3: avoid "%r" for list of byte strings, which produces b'' on py3

py3: avoid "%r" for byte string, which produces b'' on py3 Replaced by "'%s'", which I think is clearer anyway.

py3: replace str(ctx) by bytes(ctx) These are all for messages to the user and we don't want unicode for that.

py3: use inspect.signature() instead of inspect.getargspec() on py3