fix include dirs in test runner

runtests.py

@@ -8,14 +8,13 @@ import os, sys, unittest, doctest
 from distutils.extension import Extension
 from Cython.Distutils import build_ext
 
-
 from distutils.dist import Distribution
 distutils_distro = Distribution()
 
 TEST_DIRS = ['compile', 'run']
 TEST_RUN_DIRS = ['run']
 
-INCLUDE_DIRS = os.getenv('INCLUDE', '').split(os.pathsep)
+INCLUDE_DIRS = [ d for d in os.getenv('INCLUDE', '').split(os.pathsep) if d ]
 CFLAGS = os.getenv('CFLAGS', '').split()
 
 class TestBuilder(object):