Supplied shell scripts will fail if spaces exist in OpenMW path

I wanted to reach out to k1ll for this on the forums, but I am not allowed to use the PM system.

The shell scripts that point to the binaries in the provided GNU/Linux tarball do not quote $GAMEDIR and thus will fail if there are any spaces in the user's path to OpenMW. Running shellcheck reveals a few more minor issues, but the $GAMEDIR one manifests itself somewhat regularly.