Travis: quicker "install"

.travis.yml

@@ -4,14 +4,14 @@ before_install: >
   travis_retry sudo apt-get install python python-setuptools
   python-virtualenv python-dev gcc swig dialog libaugeas0 libssl-dev
 
-install:
-  - travis_retry python setup.py dev  # installs tox
-  - travis_retry pip install coveralls
-
-script: travis_retry tox
+install: "travis_retry pip install tox coveralls"
+script: "travis_retry tox"
 
 after_success: coveralls
 
+# using separate envs with different TOXENVs creates 4x1 Travis build
+# matrix, which allows us to clearly distinguish which component under
+# test has failed
 env:
   - TOXENV=py26
   - TOXENV=py27