OSspecific: altered file tests

- removed the previously added fileName type(), isDir(), isFile() methods.

- added optional bool parameter to isFile() function to explicitly
  enable/disable the check for gzip files.

- fixed minor bugginess where the default usage of isFile() would result in
  false positive matches.

- be slightly more stringent and use isDir() and isFile() instead of
  exists() function when we actually know the expected type.

applications/utilities/mesh/manipulation/setSet/setSet.C

@@ -746,7 +746,8 @@ int main(int argc, char *argv[])
 
         Pout<< "Reading commands from file " << batchFile << endl;
 
-        if (!exists(batchFile))
+        // we also cannot handle .gz files
+        if (!isFile(batchFile, false))
         {
             FatalErrorIn(args.executable())
                 << "Cannot open file " << batchFile << exit(FatalError);