Switch to a WinRPM binary

This fixes https://github.com/simonster/MAT.jl/issues/32. The previous mingw hdf5 binary I found was not built with zlib support for the deflate filter, which is used by Matlab.

I also reorganized the BinDeps style to use the `deps/deps.jl` method instead of modifying `DL_LOAD_PATH`. This will need a little bit of testing to make sure it doesn't break anything on Mac or Linux. My cross-compiled packages for both 32 and 64 bit were accepted in the official opensuse mingw project, but apparently every other package in the same project needs to finish building before the repository with the updated rpm metadata gets officially published. Once that's ready we can delete the line that modifies `WinRPM.sources`. (I can rebase it out, apparently it didn't work on AppVeyor anyway...)