formatter: add argument to change output file of non-plain formatter This allows us to build data not written to the console. That would be doable by ui.pushbuffer()/popbuffer(), but changing the file object seems cleaner.

schemes: move re construction to module-level and python3-ify This makes the schemes extension load correctly in Python 3.

dispatch: cope with sys.version being unicode on Python 3

dispatch: allow testedwith to be bytes or str

ui: fix ui.traceback on Python 3

ui: fix opts labeling on ui.warn et al for Python 3 This is a step towards fixing extension load warnings on Python 3. Note that I suspect there are still some bugs in this area and that things like color won't work, but the code at least executes and prints text to the console correctly now.

config: add sanity assert that files are opened as binary This helps with some debugging in Python 3, and shouldn't hurt anything in Python 2. The unusual construction using getattr is done so that StringIO/BytesIO instances can be used as well as real files.