Adjust rcache framework to allow hooking madvise properly

[jsquyres]

Per all the hubaloo from #1654 and #3013, @hjelmn's conclusion was that the current structure of the rcache framework will not allow us to hook madvise(2) safely. Hence, the current tip of master/v2.0.x/v2.x/v3.x (as of March 2017) is that we hook everything except madvise(2).

This issue is a placeholder for someone to re-jigger the rcache framework to allow hooking madvise(2) properly.