Add quiet_system

Same as Kernel.system, but prints no output.

Library/Homebrew/utils.rb

@@ -84,16 +84,31 @@ def interactive_shell
   end
 end
 
-# Kernel.system but with exceptions
-def safe_system cmd, *args
+module Homebrew
+  def self.system cmd, *args
     puts "#{cmd} #{args*' '}" if ARGV.verbose?
     fork do
+      yield if block_given?
       args.collect!{|arg| arg.to_s}
       exec(cmd, *args) rescue nil
       exit! 1 # never gets here unless exec failed
     end
     Process.wait
-  raise ExecutionError.new(cmd, args, $?) unless $?.success?
+    $?.success?
+  end
+end
+
+# Kernel.system but with exceptions
+def safe_system cmd, *args
+  raise ExecutionError.new(cmd, args, $?) unless Homebrew.system(cmd, *args)
+end
+
+# prints no output
+def quiet_system cmd, *args
+  Homebrew.system(cmd, *args) do
+    $stdout.close
+    $stderr.close
+  end
 end
 
 def curl *args