mysql-cluster: use install_symlink

Formula/mysql-cluster.rb

@@ -100,14 +100,14 @@ class MysqlCluster < Formula
     rm_rf prefix+'data'
 
     # Link the setup script into bin
-    ln_s prefix+'scripts/mysql_install_db', bin+'mysql_install_db'
+    bin.install_symlink prefix/"scripts/mysql_install_db"
     # Fix up the control script and link into bin
     inreplace "#{prefix}/support-files/mysql.server" do |s|
       s.gsub!(/^(PATH=".*)(")/, "\\1:#{HOMEBREW_PREFIX}/bin\\2")
       # pidof can be replaced with pgrep from proctools on Mountain Lion
       s.gsub!(/pidof/, 'pgrep') if MacOS.version >= :mountain_lion
     end
-    ln_s "#{prefix}/support-files/mysql.server", bin
+    bin.install_symlink prefix/"support-files/mysql.server"
 
     # Move mysqlaccess to libexec
     libexec.mkpath