If pico_setup.sh fails during install it can't be re-run

If you get any failure attempting to run pico-setup.sh then that script can't be rerun.

It barfs on

```
# Build a couple of examples
cd "$OUTDIR/pico-examples"
mkdir build
cd build
```

The quick hack to get round that is
```
# Build a couple of examples
cd "$OUTDIR/pico-examples"
#mkdir build
cd build
```

but it really should include code to allow a sane re-run.