title: How to support NSCalendar with both iOS 7 and 8?
body: <p>iOS 8 introduced some new values for old methods.
  For instance, creating a calendar used to be like this:</p>
  
  <pre><code>NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
  </code></pre>
  
  <p>Now, the calendar identifier has changed and I should create the object like so:</p>
  
  <pre><code>NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
  </code></pre>
  
  <p>Thing is, the compiler warns me only in the first situation that NSGregorianCalendar is deprecated. However, The compiler doesn't warn me at all about NSCalendarIdentifierGregorian compatibility with iOS 7.<br/>
  <strong>Does it mean that NSCalendarIdentifierGregorian works under iOS 7 either?</strong><br/>
  If not, what's the best way of creating a calendar with a calendar identifier depending on the OS? checking OS version every single time seems tedious.<br/><br/>
  Thank you.</p>