Add MacOS.prefer_64_bit?

Moved snow_leopard_64? to compatibility and replaced it with
a function MacOS.prefer_64_bit?. This method is in a better
place and has a better name once Lion comes out.

Fixes Homebrew/homebrew#4710

Library/Homebrew/compatibility.rb

@@ -1,3 +1,4 @@
+## Compatibility layer introduced in 0.8 (refactor)
 
 # maybe never used by anyone, but alas it must continue to exist
 def versions_of(keg_name)
@@ -50,6 +51,10 @@ def search_brews text
   Homebrew.search_brews text
 end
 
+def snow_leopard_64?
+  MacOS.prefer_64_bit?
+end
+
 class Formula
   # in compatability because the naming is somewhat confusing
   def self.resolve_alias name

Library/Homebrew/hardware.rb

@@ -69,7 +69,3 @@ protected
     $?.success? && result == 1 # sysctl call succeded and printed 1
   end
 end
-
-def snow_leopard_64?
-  MACOS_VERSION >= 10.6 and Hardware.is_64_bit?
-end

Library/Homebrew/utils.rb

@@ -301,6 +301,10 @@ module MacOS extend self
 
     false
   end
+
+  def prefer_64_bit?
+    MACOS_VERSION >= 10.6 and Hardware.is_64_bit?
+  end
 end
 
 module GitHub extend self