SSLTmpDhCallback for configuration option.
* lib/drb/ssl.rb (setup_ssl_context): copy the value of tmp_dh_callback.
* test/drb/ut_array_drbssl.rb: set tmp_dh_callback to suppress warning.
* test/drb/ut_drb_drbssl.rb: ditto.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@36999 b2dd03c8-39d4-4d8f-98ff-823fe69b080e