Added back support for :delete_old option and wrote tests for :versions option on GridFilesystem.

lib/mongo/gridfs/grid_file_system.rb

@@ -97,7 +97,12 @@ module Mongo
     def open(filename, mode, opts={})
       opts = opts.dup
       opts.merge!(default_grid_io_opts(filename))
-      versions  = opts.delete(:versions) && mode == 'w'
+      if mode == 'w'
+        versions = opts.delete(:versions)
+        if opts.delete(:delete_old) || (versions && versions < 1)
+          versions = 1
+        end
+      end
       file = GridIO.new(@files, @chunks, filename, mode, opts)
       return file unless block_given?
       result = nil

test/grid_file_system_test.rb

@@ -165,6 +165,18 @@ class GridFileSystemTest < Test::Unit::TestCase
            assert_equal 0, @db['fs.chunks'].find({'files_id' => {'$in' => @ids}}).count
          end
 
+         should "delete all versions which exceed the number of versions to keep specified by the option :versions" do
+           @versions = 1 + rand(4-1)
+           @grid.open('sample', 'w', :versions => @versions) do |f|
+             f.write @new_data
+           end
+           @new_ids = @db['fs.files'].find({'filename' => 'sample'}).map {|file| file['_id']}
+           assert_equal @versions, @new_ids.length
+           id = @new_ids.first
+           assert !@ids.include?(id)
+           assert_equal @versions, @db['fs.files'].find({'filename' => 'sample'}).count
+         end
+         
          should "delete old versions on write with :delete_old is passed in" do
            @grid.open('sample', 'w', :delete_old => true) do |f|
              f.write @new_data