Make some constant strings into actual constants

We only need one copy of each of these strings, not ~7500.

Library/Homebrew/cmd/bottle.rb

@@ -9,7 +9,7 @@ require 'extend/pathname'
 
 BOTTLE_ERB = <<-EOS
   bottle do
-    <% if  root_url != BottleSpecification.new.root_url %>
+    <% if  root_url != BottleSpecification::DEFAULT_ROOT_URL %>
     root_url "<%= root_url %>"
     <% end  %>
     <% if  prefix.to_s != "/usr/local" %>

Library/Homebrew/software_spec.rb

@@ -148,14 +148,18 @@ class Bottle
 end
 
 class BottleSpecification
+  DEFAULT_PREFIX = "/usr/local".freeze
+  DEFAULT_CELLAR = "/usr/local/Cellar".freeze
+  DEFAULT_ROOT_URL = "https://downloads.sf.net/project/machomebrew/Bottles".freeze
+
   attr_rw :root_url, :prefix, :cellar, :revision
   attr_reader :checksum, :collector
 
   def initialize
     @revision = 0
-    @prefix = '/usr/local'
-    @cellar = '/usr/local/Cellar'
-    @root_url = 'https://downloads.sf.net/project/machomebrew/Bottles'
+    @prefix = DEFAULT_PREFIX
+    @cellar = DEFAULT_CELLAR
+    @root_url = DEFAULT_ROOT_URL
     @collector = BottleCollector.new
   end