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

autopep8 -v -j 8 --max-line-length 120 --in-place --recursive

... 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/

W291 trailing whitespace

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