DYLD_FALLBACK_LIBRARY_PATH does not work for sub-processes with MacOS X 10.11

At the moment, Travis uses MacOS 10.9 by default. However, once it changes to 10.11, we'll start to see issues with recipes that need DYLD_FALLBACK_LIBRARY_PATH to be set for e.g. `configure`, because this and some other variables get purged before running such sub-processes:

http://apple.stackexchange.com/questions/212945/unable-to-set-dyld-fallback-library-path-in-shell-on-osx-10-11-1

This is already causing issues because I can't actually get things to build locally when they build fine on Travis:

https://github.com/open-mpi/ompi/issues/2068

This is just a heads-up that we should make sure we find a solution that works for the different packages. It looks like doing:

```
./configure ... LD_LIBRARY_PATH=$LD_LIBRARY_PATH
```

might work for instance.