w3m: build isn't parallel safe

Formula/w3m.rb

@@ -3,7 +3,7 @@ require 'formula'
 class W3m < Formula
   homepage 'http://w3m.sourceforge.net/'
   url 'http://downloads.sourceforge.net/project/w3m/w3m/w3m-0.5.3/w3m-0.5.3.tar.gz'
-  md5 '1b845a983a50b8dec0169ac48479eacc'
+  sha1 '444b6c8cf7094ee95f8e9de96b37f814b9d83237'
 
   depends_on 'bdw-gc'
 
@@ -19,6 +19,9 @@ class W3m < Formula
 
   def install
     system "./configure", "--prefix=#{prefix}", "--disable-image"
+    # Race condition in build reported in:
+    # https://github.com/mxcl/homebrew/issues/12854
+    ENV.j1 #
     system "make install"
   end
 end