fix for python 3.6 where DLFCN was removed

[veprbl]

No description provided.

[giovtorres]

Hi. I would be more inclined to use ctypes.RTLD_GLOBAL instead of the os.RTLD_GLOBAL module. This way, it would be supported from python 2.6 through 3.6. This is what I have in the dev branch and hasn't made it yet into master. Thoughts?

[veprbl]

When preparing this PR I was looking to minimize possible breakage. I now did a small test to see if additionally importing ctypes will take more time and didn't see any significant overhead, so, I guess, that ctypes can be very well used instead, especially if it has better compatibility.

[giovtorres]

I updated __init__.py in 9004364. Give it a try. Thanks.

[veprbl]

Thank you!