interpreter: mayExit return boolean instead of Exit(0)
interpreter: mayExit return boolean instead of Exit(0)

Fixes issue #54

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