Set "usedevelop" in tox.ini

Recreating the sdist tarball takes some time when calling tox. So skip
the sdist creation (which will be implicitly done when
"usedevelop=True" is set) and do the "setup.py develop" step instead
which is recommended in the tox documentation[1].

[1]
http://tox.readthedocs.io/en/latest/example/general.html#avoiding-expensive-sdist

1 files changed, 1 insertions, 0 deletions

diff --git a/tox.ini b/tox.ini
index e1d97c4..5cf02a6 100644
--- a/tox.ini
+++ b/tox.ini
@@ -7,6 +7,7 @@ envlist = py27,py34,flake8
 skip_missing_interpreters = True
 
 [testenv]
+usedevelop = True
 changedir = tests
 commands =
     py.test {posargs}