Fix compatibility with matlab 2016a in installer and mex-folder

I had to revert commit 6072aa0b (which is PR #1144 by @JohannesPfeifer) because the snapshot build failed this evening. The generated mex files are not saved in the expected directory. They are saved in mex/matlab/win64-7.8-8.6 instead of mex/matlab/win64-7.8-9.0. I did not find where the name of this directory is controlled. @houtanb can you fix this?