IDE: prevent multiple bad name notifications.

This patch will prevent the IDE from informing the user about a bad
sketch folder name multiple times.

Now the user is informed once at start up only, or once when it is
detected during a rescan of the folders.

Author: Chris--A

arduino-core/src/cc/arduino/contributions/libraries/LibrariesIndexer.java

@@ -57,6 +57,8 @@ public class LibrariesIndexer {
   private final File indexFile;
   private final File stagingFolder;
   private File sketchbookLibrariesFolder;
+  
+  private static List<String> badLibNotified;
 
   public LibrariesIndexer(File preferencesFolder) {
     indexFile = new File(preferencesFolder, "library_index.json");
@@ -117,11 +119,18 @@ private void scanInstalledLibraries(File folder, boolean isSketchbook) {
 
     for (File subfolder : list) {
       if (!BaseNoGui.isSanitaryName(subfolder.getName())) {
-        String mess = I18n.format(_("The library \"{0}\" cannot be used.\n"
+
+        // Detect whether the current folder name has already had a notification.
+        if(!badLibNotified.contains(subfolder.getName())) { 
+
+          badLibNotified.add(subfolder.getName());
+
+          String mess = I18n.format(_("The library \"{0}\" cannot be used.\n"
                         + "Library names must contain only basic letters and numbers.\n"
                         + "(ASCII only and no spaces, and it cannot start with a number)"),
                 subfolder.getName());
-        BaseNoGui.showMessage(_("Ignoring bad library name"), mess);
+          BaseNoGui.showMessage(_("Ignoring bad library name"), mess);
+        }
         continue;
       }