bin/buildout should touch files that are up-to-date

[Marius Gedminas]

It's convenient to have a Makefile that runs buildout on demand, e.g.

    all: bin/myapp
    run:
        bin/myapp --serve development.ini # or something
    bin/myapp: bin/buildout buildout.cfg setup.cfg
        bin/buildout
    bin/buildout: bootstrap.py
        python bootstrap.py

This fails when you have multiple parts in your buildout.cfg, and buildout (correctly) decides some of the parts haven't changed. Since buildout doesn't rewrite scripts in bin/ in that case, make thinks they're not up to date and keeps running bin/buildout again and again.

Buildout should update the file modification times (for path in paths_not_built: os.utime(path, None)).