create a separate requirements file for travis - without pytest-benchmark

pytest-benchmark (and its dependency "statistics") needs py 3.3+.

we do not want to run benchmarks on travis anyway, but even its presence
makes trouble due to this, so we just remove it from there again.

as --benchmark-skip is also removed from tox configuration, this means benchmarks
are run by default when pytest-benchmark is installed.

.travis/install.sh

@@ -43,6 +43,6 @@ fi
 
 python -m virtualenv ~/.venv
 source ~/.venv/bin/activate
-pip install -r requirements.d/development.txt
+pip install -r requirements.d/travis.txt
 pip install codecov
 pip install -e .

requirements.d/travis.txt

@@ -0,0 +1,5 @@
+tox
+mock
+pytest
+pytest-cov<2.0.0
+Cython

tox.ini

@@ -11,6 +11,6 @@ changedir = {toxworkdir}
 deps =
      -rrequirements.d/development.txt
      attic
-commands = py.test --cov=borg --benchmark-skip --pyargs {posargs:borg.testsuite}
+commands = py.test --cov=borg --pyargs {posargs:borg.testsuite}
 # fakeroot -u needs some env vars:
 passenv = *