title: setprecision for boost::program_options
body: <p>Is there a way to change how boost::program_options formats the default value of the options in the help text of a <code>program_options::options_description</code> (that one can obtains through <code>cout &lt;&lt; description</code>)?  In particular I have default values which are floats, so the usual decimal-to-binary conversion gives me a help text that looks like <code>--arg (0.100000001)</code> which is quite ugly.</p>
  
  <p>Using <code>cout &lt;&lt; setprecision(4)</code> doesn't work because program_options is <code>&lt;&lt;</code>'ing itself the default values to some internal streams to do the formatting first (at least that's what I inferred by looking at the source code), and what gets <code>&lt;&lt;</code>'ed to <code>cout</code> is the resulting string(stream?).</p>
  
  <p>Thanks.</p>