Mark fields storing keys in IncOptions as private.
Mark fields storing keys in IncOptions as private.

It was an omission in the original commit that introduced them and didn't
mark them as private. They are purely an implementation detail and should
be hidden. We hiding them now.

jkinkead/sbt,xeno-by/old-scalameta-sbt,sbt/sbt,sbt/sbt,som-snytt/xsbt,xeno-by/old-scalameta-sbt,jaceklaskowski/sbt,jkinkead/sbt,xuwei-k/xsbt,twitter-forks/sbt,dyx/sbt,Sciss/sbt,xeno-by/old-scalameta-sbt,jkinkead/sbt,jaceklaskowski/sbt,xeno-by/old-scalameta-sbt,mdedetrich/sbt,mdedetrich/sbt,jkinkead/sbt,adriaanm/sbt,mdedetrich/sbt,mdedetrich/sbt,xeno-by/old-scalameta-sbt,jaceklaskowski/sbt,twitter-forks/sbt,jasonchaffee/sbt,mdedetrich/sbt,Duhemm/compiler-bridge,mdedetrich/sbt,xuwei-k/xsbt,dyx/sbt,sbt/sbt,dyx/sbt,jaceklaskowski/sbt,sbt/sbt,pocketberserker/sbt,sbt/sbt,twitter-forks/sbt,jkinkead/sbt,Duhemm/sbt,Duhemm/sbt,dansanduleac/sbt,mdedetrich/sbt,twitter-forks/sbt,xuwei-k/xsbt,xeno-by/old-scalameta-sbt,dyx/sbt,sbt/sbt,pdalpra/sbt,jaceklaskowski/sbt,twitter-forks/sbt,xuwei-k/xsbt,xuwei-k/xsbt,dyx/sbt,corespring/sbt,sbt/sbt