Include paver in tox env - a few tests use it.

requirements/edx/paver.txt

 # Requirements to run and test Paver
 Paver==1.2.4
-lazy==1.1
-path.py==8.2.1
-watchdog==0.8.3
-python-memcached
 libsass==0.10.0

tox.ini

@@ -15,6 +15,8 @@ deps =
     -rrequirements/edx/local.txt
     -rrequirements/edx/base.txt
     -rrequirements/edx/development.txt
+    # There's 1-2 tests which call a paver command...
+    -rrequirements/edx/paver.txt
     -rrequirements/edx/testing.txt
     -rrequirements/edx/post.txt