Make SourceFile equals depend on file

Used to depend on file's path, but that does not work for VirtualFiles
that might be different even though they have the same path.

Author: odersky

compiler/src/dotty/tools/dotc/util/SourceFile.scala

@@ -54,10 +54,10 @@ class SourceFile(val file: AbstractFile, computeContent: => Array[Char]) extends
   override def jfile: Optional[JFile] = Optional.ofNullable(file.file)
 
   override def equals(that : Any): Boolean = that match {
-    case that : SourceFile => file.path == that.file.path && start == that.start
+    case that : SourceFile => file == that.file && start == that.start
     case _ => false
   }
-  override def hashCode: Int = file.path.## + start.##
+  override def hashCode: Int = file.hashCode * 41 + start.hashCode
 
   def apply(idx: Int): Char = content().apply(idx)