Add python code checkers to travis build process

.travis.yml

@@ -16,6 +16,8 @@ install:
     - sudo apt-get install $PYTHON-scipy
     - sudo apt-get install $PYTHON-setuptools
     - sudo apt-get install $PYTHON-nose
+    - sudo apt-get install pep8
+    - sudo apt-get install pyflakes
     - sudo easy_install$PYSUF pip
     - sudo pip-$PYVER install cython
     - sudo apt-get install libfreeimage3
@@ -32,3 +34,7 @@ script:
     - cd ..
     - "echo 'backend : Agg' > matplotlibrc"
     - for f in doc/examples/*.py; do $PYTHON "$f"; if [ $? -ne 0 ]; then exit $?; fi done
+    - echo "### pyflakes ###"
+    - pyflakes skimage
+    - echo "### pep8 ###"
+    - "pep8 skimage"