The only reason I bothered to make executable versions of the demo scripts was that is made it easier to write `check_yaml` work in the case where the executable might not be just `python`.  I figured out a nicer (IMO) way to do this with the new `installed_python` script, which uses the correct installed python and just calls the rest of the arguments with that version.  So `check_yaml` now uses that.

This also means that `scons examples` is not required for `check_yaml` to work anymore, which is another nice feature.

So, since we don't need to build the executables `bin/demo1`, etc., it didn't seem worth having the workaround for the case where someone might decide to run that program from within the `bin` directory.  

However, if you want to keep the `../examples/data` stuff in there, I can revert it.  It just seems a little silly considering that we tell them to run the scripts from the `examples` directory by typing `python demo1.py`, in which case it isn't necessary.