Overhaul GetPrerequisites and BundleUtilities: make fixup_bundle do something useful on Windows and Linux.

Formerly, fixup_bundle was useful only on the Mac for making standalone bundle applications that could be drag-n-drop moved to anyplace in the file system. fixup_bundle is not just for the Mac any more. It will now analyze executable files on Windows and Linux, too, and copy necessary non-system dlls to the same folder that the executable is in. This should work with dlls that you build as part of your build and also with 3rd-party dlls as long as you give fixup_bundle the right list of directories to search for those dlls. Many thanks to Clinton Stimpson for his help in ironing out the details involved in making this work.