Add -Ywarn-unused & -Ywarn-unused-import, & fix warnings

internal/util-complete/src/main/scala/sbt/internal/util/LineReader.scala

@@ -5,9 +5,8 @@ package sbt.internal.util
 
 import jline.console.ConsoleReader
 import jline.console.history.{ FileHistory, MemoryHistory }
-import java.io.{ File, InputStream, PrintWriter, FileInputStream, FileDescriptor, FilterInputStream }
+import java.io.{ File, InputStream, FileInputStream, FileDescriptor, FilterInputStream }
 import complete.Parser
-import java.util.concurrent.atomic.AtomicBoolean
 import scala.concurrent.duration.Duration
 import scala.annotation.tailrec
 

internal/util-complete/src/main/scala/sbt/internal/util/complete/EditDistance.scala

@@ -23,7 +23,6 @@ object EditDistance {
     for (i <- 1 to n; s_i = s(i - 1); j <- 1 to m) {
       val t_j = t(j - 1)
       val cost = if (s_i == t_j) matchCost else if (lower(s_i) == lower(t_j)) caseCost else subCost
-      val tcost = if (s_i == t_j) matchCost else transposeCost
 
       val c1 = d(i - 1)(j) + deleteCost
       val c2 = d(i)(j - 1) + insertCost
@@ -39,4 +38,4 @@ object EditDistance {
 
     d(n)(m)
   }
-}
+}

internal/util-complete/src/main/scala/sbt/internal/util/complete/HistoryCommands.scala

@@ -4,7 +4,6 @@
 package sbt.internal.util
 package complete
 
-import java.io.File
 import sbt.io.IO
 
 object HistoryCommands {

internal/util-complete/src/main/scala/sbt/internal/util/complete/JLineCompletion.scala

@@ -5,7 +5,7 @@ package sbt.internal.util
 package complete
 
 import jline.console.ConsoleReader
-import jline.console.completer.{ CandidateListCompletionHandler, Completer, CompletionHandler }
+import jline.console.completer.{ Completer, CompletionHandler }
 import scala.annotation.tailrec
 import collection.JavaConversions