ISSUE-34 Fix build across os platforms

The preverify step was failing on non-OSX platforms because the `sunspotfrcsdk/bin/preverify` executable was copied during NetBeans installation (on my Mac) from the `sunspotfrcsdk/platform-specific/macosx-x86` directory. We want to use the `sunspotfrcsdk` files on all platforms, so these changes alter the Ant build process to determine the platform OS and use the appropriate platform-specific `preverify` executable under the `sunspotfrcsdk/platform-specific` directories.

The changes were made in the `sunspotfrcsdk/build.xml` file so that all projects will work without changes. Additionally, the `sunspotfrcsdk/platform-specific/*/preverify` files all had to be made executable so Ant can call them.

This change means that as soon as the developers get this latest fix, then everyone should be able to build and deploy the robot on Mac OS X, Linux, or Windows.