All performance tests still print to stderr, but do so in a py3 compatible way

There is more work to do though, as many imports are still incorrect.
Also, there are still print statements

... and be able to run performance tests independently of the chosen performance test repo
Now all tests run fine locally

* travis configuration adjusted to hopefully work better than before

Performance traversal still fails when using git-python as standard repository.
It naturally wants a larger one. On travis these tests are skipped though.

Commandline was
autopep8 -j 8 --max-line-length 120 --in-place --recursive --exclude "*gitdb*,*async*" git/

E201 whitespace after '('
E202 whitespace before ')'
E203 whitespace before ':'
E225 missing whitespace around operator
E226 missing whitespace around arithmetic operator
E227 missing whitespace around bitwise or shift operator
E228 missing whitespace around modulo operator
E231 missing whitespace after ','
E241 multiple spaces after ','
E251 unexpected spaces around keyword / parameter equals

W191 indentation contains tabs
E221 multiple spaces before operator
E222 multiple spaces after operator
E225 missing whitespace around operator
E271 multiple spaces after keyword
W292 no newline at end of file
W293 blank line contains whitespace
W391 blank line at end of file