use travis python 2.7 and wheel house

tools/travis_before_install.sh

@@ -1,13 +1,15 @@
 #!/usr/bin/env bash
 set -ex
 
-export WHEELHOUSE="--no-index --find-links=http://travis-wheels.scikit-image.org/"
+export WHEELHOUSE="--no-index --trusted-host travis-wheels.scikit-image.org \
+                   --find-links=http://travis-wheels.scikit-image.org/"
 export COVERALLS_REPO_TOKEN=7LdFN9232ZbSY3oaXHbQIzLazrSf6w2pQ
 export PIP_DEFAULT_TIMEOUT=60
 sh -e /etc/init.d/xvfb start
 export DISPLAY=:99.0
 export PYTHONWARNINGS="all"
-export TEST_ARGS="--exe --ignore-files=^_test -v --with-doctest --ignore-files=^setup.py$"
+export TEST_ARGS="--exe --ignore-files=^_test -v --with-doctest \
+                  --ignore-files=^setup.py$"
 export WHEELBINARIES="matplotlib numpy scipy pillow cython"
 
 
@@ -29,20 +31,18 @@ retry () {
 }
 
 
-# on Python 2.7, use the system versions of numpy, scipy, and matplotlib
-# and the minimum version of cython and networkx
+# test with minimum requirements on 2.7
 if [[ $TRAVIS_PYTHON_VERSION == 2.7* ]]; then
-    virtualenv --system-site-packages ~/venv
-    sudo apt-get install python-scipy python-matplotlib python-imaging
-    sed -i 's/cython>=/cython==/g' requirements.txt
-    sed -i 's/networkx>=/networkx==/g' requirements.txt
+    sed -i 's/>=/==/g' requirements.txt
+    # PIL instead of Pillow
     sed -i '/pillow/d' requirements.txt
-    export WHEELBINARIES=${WHEELBINARIES/pillow/}
-else
-    virtualenv -p python --system-site-packages ~/venv
+    export WHEELBINARIES=${WHEELBINARIES/pillow/pil}
 fi
 
+# create new empty venv
+virtualenv -p python ~/venv
 source ~/venv/bin/activate
+
 retry pip install wheel flake8 coveralls nose
 
 # install system tk for matplotlib
@@ -51,7 +51,7 @@ sudo apt-get install python-tk
 
 # on Python 3.2, use matplotlib 1.3.1
 if [[ $TRAVIS_PYTHON_VERSION == 3.2 ]]; then
-    sed -i 's/matplotlib>=*.*.*/matplotlib==1.3.1/g' requirements.txt
+    sed -i 's/matplotlib>=.*/matplotlib==1.3.1/g' requirements.txt
 fi
 
 retry pip install $WHEELHOUSE $WHEELBINARIES