migrates to 2.11.0-RC1
using compat._ to plug source compatibility breakages
removes logic that branches on forInteractive
compat => internal
injects context into AsyncBase
abort => c.abort
currentUnit.freshName => c.freshName (leads to less precise tests...)
removes "import global._" and "def Expr" in TransformUtils
eliminates all usages of global in TransformUtils
cleans up LiveVariables
cleans up Lifter
cleans up FutureSystem
cleans up ExprBuilder
cleans up AsyncTransform
cleans up AsyncAnalysis
cleans up AnfTransform
gets rid of home-grown changeOwner
replaces mkAttributedCast
migrates transformAt to typingTransform
migrates UseFields to typingTransform