Unconfuse error message

When a core directory without boards.txt file was encountered, the IDE
would show:

	Could not find boards.txt in /path/to/core/boards.txt.  Is it pre-1.5?

Which appears confusing: Is it looking inside a directory called
boards.txt? Now this is improved to:

	Could not find boards.txt in /path/to/core/.  Is it pre-1.5?

which makes a lot more sense.

Author: matthijskooijman

app/src/processing/app/debug/TargetPlatform.java

@@ -71,7 +71,7 @@ public TargetPlatform(String _name, File _folder, TargetPackage parent)
     if (!boardsFile.exists() || !boardsFile.canRead())
       throw new TargetPlatformException(
           format(_("Could not find boards.txt in {0}. Is it pre-1.5?"),
-                 boardsFile.getAbsolutePath()));
+                 folder.getAbsolutePath()));
 
     // Load boards
     try {