Make tox use lib-verify

The tox config previously had a copy of the same set of skipped checks
as the Travis verify functions.  In order to avoid issues in the future,
it now just calls into that.

Author: DirectXMan12

.travis/lib-verify.sh

@@ -11,7 +11,7 @@ verify::flake8() {
     # E225: missing whitespace around operator
     # E226: missing whitespace around arithmetic operator
     # E227: missing whitespace around bitwise or shift operator
-    # E402: module level import not at top of file
+    # E402: module level import not at top of file (needed for the `GSSAPI="blah" lines)
     # E901: SyntaxError or IndentationError
     # E999: Internal AST compilation error (flake8 specific)
     flake8 gssapi --filename='*.pyx,*.pxd' --ignore=E225,E226,E227,E402,E901,E999

tox.ini

@@ -7,12 +7,9 @@
 envlist = py27,py33,py34,py35
 
 [testenv]
-# NB(sross): disabling E225,E226,E227,E901 make pep8 think Cython is ok
-# NB(sross): disable E402 because of the GSSAPI="blah" lines needed by Cython
+whitelist_externals=bash
 commands =
-    flake8 setup.py
-    flake8 gssapi
-    flake8 gssapi --filename='*.pyx,*.pxd' --ignore=E225,E226,E227,E901,E402
+    bash -c "source ./.travis/lib-verify.sh && verify::flake8"
     python setup.py nosetests []
 
 deps = -r{toxinidir}/test-requirements.txt