make symlinks relocatable

[Michael-Hennecke]

When creating symlinks like schema-tools, currently absolute paths are used. It would be really useful if those could be changed to relative paths, so the IO500 directory as a whole can be easily relocated to another directory path without breaking the links. For example:

ln -f -s build/cdcl-schema-tools ./schema-tools

(In many early-deployment environments the IO500 code needs to be downloaded on another computer and then copied onto the machine, often under a different path.)

Thanks,
-Michael Hennecke