Try shell magic instead of the download_binary action.

Dave's clever plan with the download_binary action should
offer us automatic installation of the NCBI binaries if
available for the architecture, falling back on compiling
from source otherwise. But it didn't work on the test
Tool Shed overnight functional tests.

This is a sneaky hack to do the platform selection with
shell commands instead.

If this works, it can be extended to add the compilation
fallback as well.
Trying binary install only again...