* lib/rubygems/config_file.rb:  Lazily load .gem/credentials to only
  check permissions when necessary.  RubyGems bug #465
* test/rubygems/test_gem_config_file.rb:  Test for the above.

* test/rubygems/test_gem_commands_push_command.rb:  Remove duplicated
  test.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39491 b2dd03c8-39d4-4d8f-98ff-823fe69b080e