Formatting fails when value-to-print is very large #607

Reproduce with:

• Start bpython (happens in both bpython version 0.15 on top of Python 3.5.1+ /usr/bin/python3 and bpython version 0.15 on top of Python 2.7.11+ /usr/bin/python)
• Do something that has at least two screenfuls of output when printed. Example: ["Hello"] * 1000

Expected result: boring stuff. Just the printed "value" of a list that contains a thousand "hello"s.

Actual result: The value, and then some formatting related characters that got garbled:

>>> ["Hello"] * 1000
['Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello',
 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello',
[... SNIP ...]
 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello',
 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello']�[-26;1H
>>>

Note the trailing U+001B which smells like formatting gone wrong.

I'm not sure whether this is a bug in xfce4-terminal 0.6.3, bpython, bpython-curtsies, curtsies, or maybe something else entirely. However, bpython is the only program exhibiting this behavior, so I reported it here.