minor: load same version on mongo_ext

lib/mongo.rb

@@ -10,6 +10,7 @@ end
 begin
     # Need this for running test with and without c ext in Ruby 1.9.
     raise LoadError if ENV['TEST_MODE'] && !ENV['C_EXT']
+    gem 'mongo_ext', "= #{Mongo::VERSION}"
     require 'mongo_ext/cbson'
     require 'mongo/util/bson_c'
     BSON            = BSON_C
@@ -21,7 +22,7 @@ begin
     warn "\n**Notice: C extension not loaded. This is required for optimum MongoDB Ruby driver performance."
     warn "  You can install the extension as follows:\n  gem install mongo_ext\n"
     warn "  If you continue to receive this message after installing, make sure that the"
-    warn "  mongo_ext gem is in your load path.  This may mean requiring rubygems.\n"
+    warn "  mongo_ext gem is in your load path and that the mongo_ext and mongo gems are of the same version.\n"
 end 
 
 require 'mongo/types/binary'
@@ -42,3 +43,4 @@ require 'mongo/db'
 require 'mongo/cursor'
 require 'mongo/collection'
 require 'mongo/admin'
+