allow query() to be called after the `req` has been created
allow query() to be called after the `req` has been created

This makes code like this work as expected:

  request.get('http://google.com')
    .set('some', 'header')
    .query({ foo: 'bar' });

It relies on the "path" property of the node request object, which is mutable
up until the HTTP headers get flushed.

deltreey/superagent,deltreey/superagent,sebastianvera/superagent,KingMario/superagent,bevacqua/superagent,ccapndave/superagent,yussan/superagent,nemisj/superagent,brotchie/superagent,stasha/superagent,noikiy/suberagent,focusaurus/superagent,eligolding/superagent,visionmedia/superagent,jarvisaoieong/superagent,kmalakoff/superagent-ls,aaroncrows/superagent,KuroGuo/suberagent,mvanlonden/superagent-webpack-client,ertrzyiks/superagent,drinks/superagent,alinz/superagent,eligolding/superagent,simonvizzini/superagent,thejameskyle/superagent,craigspaeth/superagent,RubenVerborgh/superagent,stanzi83/superagent,brainbytes/superagent,stanzi83/superagent,KuroGuo/suberagent,yussan/superagent,noikiy/suberagent,wushuyi/superagent,philipshurpik/superagent,reinaldo13/superagent,h1bomb/superagent,brotchie/superagent,simonvizzini/superagent,ertrzyiks/superagent,geminiyellow/superagent,stasha/superagent,ccapndave/superagent,classdojo/superagent,craigspaeth/superagent,RubenVerborgh/superagent,brainbytes/superagent,andyburke/superagent,killerlayup/superagent,sebastianvera/superagent,modulexcite/superagent,kmalakoff/superagent-ls,reinaldo13/superagent,alinz/superagent,fredigato/superagent,wushuyi/superagent,soyuka/superagent,thejameskyle/superagent,fredigato/superagent,focusaurus/superagent,jarvisaoieong/superagent,targos/superagent,puterakahfi/superagent,killerlayup/superagent,modulexcite/superagent,KingMario/superagent,philipshurpik/superagent,visionmedia/superagent,visionmedia/superagent,yeatszhang/superagent,zsh2938/superagent,h1bomb/superagent,classdojo/superagent,andyburke/superagent,drinks/superagent,aaroncrows/superagent,geminiyellow/superagent,targos/superagent,sutoiku/superagent,yeatszhang/superagent,nemisj/superagent,mvanlonden/superagent-webpack-client,soyuka/superagent,zsh2938/superagent,puterakahfi/superagent,sutoiku/superagent