report exception when file cannot be read in ConfigMerge tool

Author: vladak

src/org/opensolaris/opengrok/configuration/ConfigMerge.java

@@ -145,7 +145,7 @@ public static void main(String[] argv) {
         try {
             cfgNew = Configuration.read(new File(argv[optind + 1]));
         } catch (IOException ex) {
-            System.err.println("cannot read file " + argv[optind + 1]);
+            System.err.println("cannot read file " + argv[optind + 1] + ":" + ex);
             System.exit(1);
         }