Draw borders before content

This reverses 8e0de9a, which I probably had a good reason for at the
time but for some reason didn't document. The behavior introduced by
that commit broke table cells inside stretchy bounds, because the
absolute location of the y-position depends on when the bounds are
stretched (prawnpdf#153).

Introduced a spec to cover the new behavior and prevent regressions.
Closes prawnpdf#153.

lib/prawn/table/cell.rb

@@ -235,13 +235,14 @@ def natural_content_height
       #
       def draw(pt=[x, y])
         set_width_constraints
+
         draw_background(pt)
+        draw_borders(pt)
         @pdf.bounding_box([pt[0] + padding_left, pt[1] - padding_top], 
                           :width  => content_width + FPTolerance,
                           :height => content_height + FPTolerance) do
           draw_content
         end
-        draw_borders(pt)
       end
 
       # x-position of the cell within the parent bounds.

spec/cell_spec.rb

@@ -332,6 +332,16 @@ def close?(actual, expected, epsilon=0.01)
       end
       @pdf.cell(:content => "text", :borders => [:right])
     end
+
+    it "should draw borders at the same location when in or out of bbox" do
+      @pdf.expects(:stroke_line).checking do |from, to|
+        @pdf.map_to_absolute(from).map{|x| x.round}.should == [36, 756]
+        @pdf.map_to_absolute(to).map{|x| x.round}.should == [65, 756]
+      end
+      @pdf.bounding_box([0, @pdf.cursor], :width => @pdf.bounds.width) do
+        @pdf.cell(:content => "text", :borders => [:top])
+      end
+    end
   end
 
   describe "Text cell attributes" do