How can I fix these non-manifold edges (boundaries prior to remove doubles, non-contiguous after remove doubles)? I am trying to create a ring for 3D printing.  Part of the requirements for 3D printing is to not have any non-manifold geometry in your model.  When checking whether I met this requirement, I found that my model contains two edge loops consisting of "Boundaries" non-manifold geometry.

Highlighted in orange are the non-manifold edges of type "boundaries" (Highlighted using Ctrl + Alt + Shift + M, only Boundaries is toggled so that I could narrow down what type of non-manifold this is):


When I zoom in and move some of these edges aside, I find that there exists a duplicate edge loop underneath!:


I undo that translation, reselect the non-manifold edge loops through Ctrl + Alt + Shift + M, and I "Remove Doubles".  Here, I find that the hidden duplicate loop no longer exists, but now my non-manifold edges are of type "Non Contiguous":


I read that non-contiguous edges are due to face normals being in opposite directions(?).  Turning on face normals, I get this:


Honestly, I am new to 3D Modelling and Blender, and am not sure how to correct my issue from here.  Do you guys have any advice?

Edit: Here is the .blend file prior to the modifications mentioned in this post:
In this case:


Select all vertices, and CtrlV .. R remove doubles
Then, with all still selected, CtrlN, make normals consistent.