Added iftop formula.

"iftop does for network usage what top does for
CPU usage. It listens to network traffic on a
named interface and displays a table of current
bandwidth usage by pairs of hosts."

Formula/iftop.rb

@@ -0,0 +1,12 @@
+require 'formula'
+
+class Iftop <Formula
+  url 'http://www.ex-parrot.com/~pdw/iftop/download/iftop-0.17.tar.gz'
+  homepage 'http://www.ex-parrot.com/~pdw/iftop/'
+  md5 '062bc8fb3856580319857326e0b8752d'
+
+  def install
+    system "./configure", "--prefix=#{prefix}", "--disable-debug", "--disable-dependency-tracking", "--mandir=#{man}"
+    system "make install"
+  end
+end