Update incremental compile debug message

sbt 0.13.1 was changed so that products were invalidated
not just when they were deleted, but also when they were
modified, however the debug message was not updated to
reflect this, causing people to think invalidated class files
had been deleted.

compile/inc/src/main/scala/sbt/inc/IncrementalCommon.scala

@@ -196,7 +196,7 @@ private[inc] abstract class IncrementalCommon(log: Logger, options: IncOptions)
       checkAbsolute(srcChanges.added.toList)
       log.debug(
         "\nInitial source changes: \n\tremoved:" + srcChanges.removed + "\n\tadded: " + srcChanges.added + "\n\tmodified: " + srcChanges.changed +
-          "\nRemoved products: " + changes.removedProducts +
+          "\nInvalidated products: " + changes.removedProducts +
           "\nExternal API changes: " + changes.external +
           "\nModified binary dependencies: " + changes.binaryDeps +
           "\nInitial directly invalidated sources: " + srcDirect +
@@ -335,4 +335,4 @@ private[inc] abstract class IncrementalCommon(log: Logger, options: IncOptions)
       }
       xs.toSet
     }
-}
+}

notes/0.13.9/debug-removed-products.markdown

@@ -0,0 +1,10 @@
+  [@jroper]: https://github.com/jroper
+  [1961]: https://github.com/sbt/sbt/issues/1961
+
+### Changes with compatibility implications
+
+### Improvements
+
+### Fixes
+
+- Correct incermental compile debug message for invalidated products [#1961][1961] by [@jroper][@jroper]