install.sh: Copy lib/freebasic/ recursively

For FB 0.90.1 copying lib/freebasic/ non-recursively was enough, but now
that there can be lib/freebasic/linux/ or lib/freebasic/x86_64-linux/ etc.
subdirectories again, we need to copy recursively, and it should work no
matter what name the lib/freebasic/<target> directory has.