add Formula.racks

Also exclude symlink when enumerating installed racks.

Library/Homebrew/cmd/cleanup.rb

@@ -31,8 +31,7 @@ module Homebrew
   end
 
   def cleanup_cellar
-    return unless HOMEBREW_CELLAR.directory?
-    HOMEBREW_CELLAR.subdirs.each do |rack|
+    Formula.racks.each do |rack|
       begin
         cleanup_formula Formulary.from_rack(rack)
       rescue FormulaUnavailableError, TapFormulaAmbiguityError

Library/Homebrew/cmd/info.rb

@@ -22,7 +22,7 @@ module Homebrew
   def print_info
     if ARGV.named.empty?
       if HOMEBREW_CELLAR.exist?
-        count = HOMEBREW_CELLAR.subdirs.length
+        count = Formula.racks.length
         puts "#{count} keg#{plural(count)}, #{HOMEBREW_CELLAR.abv}"
       end
     else

Library/Homebrew/cmd/linkapps.rb

@@ -1,5 +1,6 @@
 # Links any Applications (.app) found in installed prefixes to /Applications
 require "keg"
+require "formula"
 
 module Homebrew
   def linkapps
@@ -12,8 +13,7 @@ module Homebrew
     end
 
     if ARGV.named.empty?
-      racks = HOMEBREW_CELLAR.subdirs
-      kegs = racks.map do |rack|
+      kegs = Formula.racks.map do |rack|
         keg = rack.subdirs.map { |d| Keg.new(d) }
         next if keg.empty?
         keg.detect(&:linked?) || keg.max { |a, b| a.version <=> b.version }

Library/Homebrew/cmd/list.rb

@@ -78,7 +78,7 @@ module Homebrew
 
   def filtered_list
     names = if ARGV.named.empty?
-      HOMEBREW_CELLAR.subdirs
+      Formula.racks
     else
       ARGV.named.map { |n| HOMEBREW_CELLAR+n }.select(&:exist?)
     end

Library/Homebrew/formula.rb

@@ -809,18 +809,23 @@ class Formula
     end
   end
 
+  # An array of all racks currently installed.
+  def self.racks
+    @racks ||= if HOMEBREW_CELLAR.directory?
+      HOMEBREW_CELLAR.subdirs.reject(&:symlink?)
+    else
+      []
+    end
+  end
+
   # An array of all installed {Formula}
   def self.installed
-    @installed ||= if HOMEBREW_CELLAR.directory?
-      HOMEBREW_CELLAR.subdirs.map do |rack|
+    @installed ||= racks.map do |rack|
       begin
         Formulary.from_rack(rack)
       rescue FormulaUnavailableError, TapFormulaAmbiguityError
       end
     end.compact
-    else
-      []
-    end
   end
 
   def self.aliases