title: equivalent of "touch" in scons?
body: <p>scons uses MD5 hashes rather than file mod times to determine if a dependency needs to be built.</p>
  
  <p>I want this to be the default behavior. But is there any way to force it to assume a particular file is out of date (the equivalent of "touch"), besides editing the file to make it different?</p>
  
  <p><strong>edit:</strong> use case:</p>
  
  <p>binary file F is used to create another file G using a tool X. For some reason file G has changed (it got corrupted, or I edited it) or tool X has changed, and I want to recreate file G and everything downstream of it.</p>
  
  <p><strong>edit:</strong> This is for occasional use only. I do not want this to happen always, only those few times when I ask for it. Also I may not know the particular file ahead of time. For this reason I do not want to modify the SConscript/SConstruct files to build a particular file. What I would like is to do this at a command prompt:</p>
  
  <pre><code>scons {something to specify file foobar.h}
  </code></pre>
  
  <p>and that would force scons to build all files depending on foobar.h, whereas just typing <code>scons</code> would do the regular build using MD5 hashes for dependency checking. I don't mind editing the SConscript/SConstruct files ahead of time to allow this (custom Decider, I guess), if there's a way to do so that doesn't significantly increase the build times.</p>