handroll for-expression
handroll for-expression

Ref https://github.com/sbt/sbt/pull/3979

Based on #3979 this handrolls the for-express using while.

sbt/sbt,sbt/sbt,mdedetrich/sbt,mdedetrich/sbt,xuwei-k/xsbt,mdedetrich/sbt,xuwei-k/xsbt,mdedetrich/sbt,sbt/sbt,sbt/sbt,xuwei-k/xsbt,sbt/sbt,mdedetrich/sbt,mdedetrich/sbt,xuwei-k/xsbt,xuwei-k/xsbt,sbt/sbt,mdedetrich/sbt,sbt/sbt