title: MacPorts: Add an option to configure script
body: <p>I am trying to install libguichan without allegro support, because allegro will not build on Snow Leopard.</p>
  
  <p>It should be left out, the portfile has:</p>
  
  <pre><code>27  if {${os.platform} == "darwin" &amp;&amp; (([variant_isset universal] &amp;&amp; [string match *64* $universal_archs]) || (![variant_isset universal] &amp;&amp; [string match *64 $build_arch]))} {
  28      # allegro is not yet 64-bit compatible
  29      depends_lib-delete port:allegro
  30      configure.args-append --disable-allegro
  31  }
  </code></pre>
  
  <p>But when I install it, it tries to build allegro. Is there any way I can get this functionality from the command line to install it?</p>
  
  <p>The port: <a href="http://trac.macports.org/browser/trunk/dports/graphics/libguichan/Portfile" rel="nofollow noreferrer">http://trac.macports.org/browser/trunk/dports/graphics/libguichan/Portfile</a></p>