plans: join filter must use origin result fields
plans: join filter must use origin result fields

Fix #363
e,g, `select * from t as a`
The plan phase in from is table plan -> join plan, and we can only get
the alias name in join plan, so if we return origin table plan directly
in join Filter, we may get wrong result fields.

JinheLin/tidb,pingcap/tidb,andelf/tidb,kyle-wang/tidb,qiuyesuifeng/tidb,ming-relax/tidb,kyle-wang/tidb,gaocegege/tidb,cosmtrek/tidb,liyu4/tidb,c4pt0r/tidb,myrice/tidb,ngaut/tidb,Cofyc/tidb,ngaut/tidb,kyle-wang/tidb,Nify/tidb,c4pt0r/tidb,CodeRushing/tidb,yuanwhy/tidb,kyle-wang/tidb,yangwenmai/tidb,louishust/tidb,anywhy/tidb,ngaut/tidb,silentred/tidb,JinheLin/tidb,mccxj/tidb,c4pt0r/tidb,pingcap/tidb,zimulala/tidb,ngaut/tidb,andelf/tidb,tiancaiamao/tidb,ngaut/tidb,XuHuaiyu/tidb,astaxie/tidb,coocood/tidb,yuanwhy/tidb,liyu4/tidb,tiancaiamao/tidb,wusphinx/tidb,c4pt0r/tidb,8cbx/tidb,spongedu/tidb,EvilMcJerkface/tidb,silenceper/tidb,ngaut/tidb,spongedu/tidb,Cofyc/tidb,yangwenmai/tidb,netroby/tidb,pingcap/tidb,louishust/tidb,c4pt0r/tidb,coocood/tidb,qhsong/tidb,kyle-wang/tidb,c4pt0r/tidb,qiuyesuifeng/tidb,8cbx/tidb,silenceper/tidb,zs634134578/tidb,zs634134578/tidb,XuHuaiyu/tidb,anywhy/tidb,cosmtrek/tidb,simon-xia/tidb,qhsong/tidb,pingcap/tidb,myrice/tidb,ueizhou/tidb,ming-relax/tidb,astaxie/tidb,pingcap/tidb,netroby/tidb,Nify/tidb,silentred/tidb,gaocegege/tidb,wusphinx/tidb,EvilMcJerkface/tidb,mccxj/tidb,zimulala/tidb,kyle-wang/tidb,CodeRushing/tidb,ueizhou/tidb,simon-xia/tidb,pingcap/tidb