render templates in the context of the package, not the source

This allows things like debs referring to x86_64 as amd64
to be in the Deb class.

lib/fpm/builder.rb

@@ -22,11 +22,6 @@ def garbage
     @garbage ||= []
   end
 
-  # the spec or control file
-  def spec
-    @spec ||= @source.render(@package.template)
-  end
-
   attr_reader :paths
   attr_reader :package
   attr_reader :source
@@ -113,7 +108,9 @@ def cleanup!
   end
 
   def generate_specfile
-    File.open(@package.specfile(builddir), "w") { |f| f.puts spec }
+    File.open(@package.specfile(builddir), "w") do |f|
+      f.puts @package.render_spec
+    end
   end
 
   def generate_md5sums

lib/fpm/package.rb

@@ -82,6 +82,10 @@ def template
     end
   end
 
+  def render_spec
+    template.result(binding)
+  end
+
   def default_output
     "#{name}-#{version}-#{iteration}.#{architecture}.#{type}"
   end

lib/fpm/source.rb

@@ -66,11 +66,6 @@ def package(pkg_cls)
     pkg_cls.new(self)
   end
 
-  # make the binding public for erb templating
-  def render(template)
-    template.result(binding)
-  end
-
 private
   def tar(output, paths)
     dirs = []