Generator: option -s (skip-unchanged) doesn't work

[erikvanoosten]

Main.scala contains the following option definition:

      opt("s", "skip-unchanged", "Don't re-generate if the target is newer than the input", { compiler.skipUnchanged = true; () })

However, the boolean compiler.skipUnchanged is never read. This function doesn't seem implemented.

[mosesn]

Indeed, we should just remove it. Or if someone is feeling ambitious, fix it!