STYLE: use string substr instead of string::operator()

- makes the purpose clearer.
  In some places, string::resize() is even simpler.

- use C++11 string::back() in preference to str[str.size()-1]

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

@@ -903,10 +903,10 @@ int main(int argc, char *argv[])
             }
 
             // Strip off anything after #
-            string::size_type i = rawLine.find_first_of("#");
+            string::size_type i = rawLine.find('#');
             if (i != string::npos)
             {
-                rawLine = rawLine(0, i);
+                rawLine.resize(i);
             }
 
             if (rawLine.empty())