Do not delete the source if source = destination

While the previous version could handle the case, it only did so after
deleting the destination file, therefore causing data loss.

app/src/processing/app/SketchController.java

@@ -495,6 +495,10 @@ public class SketchController {
       isData = true;
     }
 
+    if (!sourceFile.equals(destFile)) {
+      // The typical case here is adding a file from somewhere else.
+      // This however fails if the source and destination are equal
+
       // check whether this file already exists
       if (destFile.exists()) {
         Object[] options = { tr("OK"), tr("Cancel") };
@@ -518,8 +522,7 @@ public class SketchController {
       // otherwise case changes will not be preserved.
       // http://dev.processing.org/bugs/show_bug.cgi?id=969
       if (replacement) {
-      boolean muchSuccess = destFile.delete();
+        if (!destFile.delete()) {
-      if (!muchSuccess) {
           Base.showWarning(tr("Error adding file"),
                            I18n.format(tr("Could not delete the existing ''{0}'' file."), filename),
                            null);
@@ -527,18 +530,7 @@ public class SketchController {
         }
       }
 
-    // make sure they aren't the same file
+      // perform the copy
-    if (isData && sourceFile.equals(destFile)) {
-      Base.showWarning(tr("You can't fool me"),
-                       tr("This file has already been copied to the\n" +
-                         "location from which where you're trying to add it.\n" +
-                         "I ain't not doin nuthin'."), null);
-      return false;
-    }
-
-    // in case the user is "adding" the code in an attempt
-    // to update the sketch's tabs
-    if (!sourceFile.equals(destFile)) {
       try {
         Base.copyFile(sourceFile, destFile);
 
@@ -549,7 +541,18 @@ public class SketchController {
         return false;
       }
     }
+    else {
+      // If the source and destination are equal, a code file is handled
+      //   - as a replacement, if there is a corresponding tab,
+      //    (eg. user wants to update the file after modifying it outside the editor)
+      //   - as an addition, otherwise.
+      //    (eg. the user copied the file to the sketch folder and wants to edit it)
+      // For a data file, this is a no-op.
+      if (editor.findTabIndex(destFile) >= 0)
+        replacement = true;
+    }
 
+    // open/refresh the tab
     if (!isData) {
       int tabIndex;
       if (replacement) {