TravisCI: Use new stages functionality.

Goal here is to run the quick packaging and style checks
as the first stage, and only if that passes proceed to
the slow functional tests.

.travis.yml

@@ -9,26 +9,42 @@
 # Environment variables setup here:
 # - TOXENV = environment used in Tox (conventionally uses py35 etc)
 #
+# TravisCI build stages used here:
+# - basics - quick things like style and packaging
+# - test - the actual functional tests which are slow
 
 language: python
 matrix:
   include:
-    - env: TOXENV=style
-    - env: TOXENV=sdist
-    - env: TOXENV=bdist_wheel
-    - python: 2.7
+    - stage: basics
+      env: TOXENV=style
+      before_install: echo "Going to run basic checks"
+    - stage: basics
+      env: TOXENV=sdist
+      before_install: echo "Going to run basic checks"
+    - stage: basics
+      env: TOXENV=bdist_wheel
+      before_install: echo "Going to run basic checks"
+    - stage: test
+      python: 2.7
       env: TOXENV=py27-cover
-    - python: 3.3
+    - stage: test
+      python: 3.3
       env: TOXENV=py33-cover
-    - python: 3.4
+    - stage: test
+      python: 3.4
       env: TOXENV=py34-cover
-    - python: 3.5
+    - stage: test
+      python: 3.5
       env: TOXENV=py35-cover
-    - python: 3.6
+    - stage: test
+      python: 3.6
       env: TOXENV=py36-cover
-    - python: pypy
+    - stage: test
+      python: pypy
       env: TOXENV=pypy-nocov
-    - python: pypy3
+    - stage: test
+      python: pypy3
       env: TOXENV=pypy3-nocov
 
 sudo: false
@@ -56,7 +72,8 @@ addons:
 #
 # We also need DSSP for testing but it is not available in the repositories.
 # Try to download the binary for Linux and place it in $HOME/bin
-# 
+#
+# This before_install list is only used for the test stage.
 before_install:
   - cd $HOME
   - mkdir bin
@@ -72,9 +89,11 @@ before_install:
   - mv dssp-2.0.4-linux-amd64 bin/dssp
   - chmod a+x bin/dssp
   - cd $TRAVIS_BUILD_DIR
+  - "cp Tests/biosql.ini.sample Tests/biosql.ini"
 
+
+# This is minimal and used under all stages
 install:
-  - "cp Tests/biosql.ini.sample Tests/biosql.ini"
   - "pip install --upgrade pip setuptools"
   - "pip install tox"
   - "tox -c .travis-tox.ini -e $TOXENV --notest"