Reworked reachability initialization to support usage when there is no Internet connectivity.

* When the reachabilityObserver property of RKClient is nil, assume we have reachability
* When the baseURL configured contains an IP address or localhost, use hostname based reachability
* Else fall through to using Internet reachability if the user has not configured an observer directly

Code/Support/NSString+RestKit.h

@@ -117,4 +117,12 @@
  */
 - (NSString *)MIMETypeForPathExtension;
 
+/**
+ Returns YES if the receiver contains a valid IP address
+ 
+ For example, @"127.0.0.1" and @"10.0.1.35" would return YES
+ while @"restkit.org" would return NO
+ */
+- (BOOL)isIPAddress;
+
 @end