Create only one undo for each save action invocation

Each changed region creates its own undo entry in the undo queue. This
means that one has to undo each text change separately after save
actions are invoked instead of only a single undo.

Fortunately it is possible to tell the undo queue that multiple undos
belong together.

org.scala-ide.sdt.core/src/org/scalaide/ui/internal/editor/SaveActionExtensions.scala

@@ -1,6 +1,7 @@
 package org.scalaide.ui.internal.editor
 
-import scala.concurrent._, ExecutionContext.Implicits.global
+import scala.concurrent._
+import scala.concurrent.ExecutionContext.Implicits.global
 import scala.concurrent.duration._
 import scala.reflect.internal.util.SourceFile
 import scala.tools.refactoring.common.{TextChange => RTextChange}
@@ -11,6 +12,7 @@ import org.eclipse.jdt.core.ICompilationUnit
 import org.eclipse.jdt.internal.ui.javaeditor.saveparticipant.IPostSaveListener
 import org.eclipse.jface.text.IDocument
 import org.eclipse.jface.text.IRegion
+import org.eclipse.text.undo.DocumentUndoManagerRegistry
 import org.scalaide.core.IScalaPlugin
 import org.scalaide.core.compiler.IScalaPresentationCompiler
 import org.scalaide.core.compiler.IScalaPresentationCompiler.Implicits._
@@ -33,9 +35,9 @@ import org.scalaide.extensions.saveactions.AutoFormattingSetting
 import org.scalaide.extensions.saveactions.RemoveDuplicatedEmptyLinesSetting
 import org.scalaide.extensions.saveactions.RemoveTrailingWhitespaceSetting
 import org.scalaide.logging.HasLogger
-import org.scalaide.util.internal.FutureUtils.TimeoutFuture
 import org.scalaide.util.eclipse.EclipseUtils
 import org.scalaide.util.eclipse.EditorUtils
+import org.scalaide.util.internal.FutureUtils.TimeoutFuture
 import org.scalaide.util.internal.eclipse.TextEditUtils
 
 object SaveActionExtensions {
@@ -100,7 +102,12 @@ trait SaveActionExtensions extends HasLogger {
    * Applies all save actions to the contents of the given document.
    */
   private def applySaveActions(udoc: IDocument): Unit = {
+    val undoManager = DocumentUndoManagerRegistry.getDocumentUndoManager(udoc)
+    undoManager.beginCompoundChange()
+
     applyDocumentExtensions(udoc)
+
+    undoManager.endCompoundChange()
   }
 
   /**