Add gzip utility function.

Library/Homebrew/utils.rb

@@ -150,6 +150,12 @@ def exec_editor *args
   exec *(editor.split+args)
 end
 
+# GZips the given path, and returns the gzipped file
+def gzip path
+  system "/usr/bin/gzip", path
+  return Pathname.new(path+".gz")
+end
+
 # returns array of architectures suitable for -arch gcc flag
 def archs_for_command cmd
     cmd = `/usr/bin/which #{cmd}` unless Pathname.new(cmd).absolute?