Fix the default return from default_blas_flags to return valid flags.

theano/tensor/blas.py

@@ -319,7 +319,9 @@ SOMEPATH/Canopy_64bit/User/lib/python2.7/site-packages/numpy/distutils/system_in
     # readily available. We try to see if that's the case, rather
     # than disable blas. To test it correctly, we must load a program.
     # Otherwise, there could be problem in the LD_LIBRARY_PATH.
-    return try_blas_flag(['-lblas'])
+    ret = try_blas_flag(['-lblas'])
+    if ret:
+        return ' '.join(ret)
 
 
 def try_blas_flag(flags):