Racket appears to have a different notion of current directory than the
system does, so we need to tell it which directory we think we're in
when reading and writing bytevectors using the scheme file functions.
Instead of dumping the required dynamic libraries in the working
directly, where the executable won't necessarily find them, take the
same approach as the Chez backend and create a subdirectory for the
required runtime files and use a shell script to start up with the right
library paths.
