should show error page content when status === 500

[fengmk2]

show error page

better than this

 $ cnpm sync octopie
Start sync ["octopie"].
logurl: http://cnpmjs.org/sync/octopie#logid=2041
[2014-01-24 14:29:49] user: fengmk2, sync octopie worker start, 1 concurrency, nodeps: false, publish: false
[2014-01-24 14:29:50] [error] [octopie] get package error: JSONResponseFormatError: Unexpected token I, GET http://registry.npmjs.org/octopie
    at Object.parse (native)
    at IncomingMessage.<anonymous> (/home/www/git/cnpmjs.org/node_modules/urllib/lib/urllib.js:334:25)
    at IncomingMessage.EventEmitter.emit (events.js:117:20)
    at _stream_readable.js:920:16
    at process._tickCallback (node.js:415:13)
[2014-01-24 14:29:50] [done] Sync octopie module finished, 0 success, 1 fail
Success: [  ]
Fail: [ octopie ]
Sync all packages done, successed: ["octopie"], failed: []

[fengmk2]