Add cancellation API to RKObjectManager.

* Introduces `cancelAllObjectRequestOperationsWithMethod:pathPattern:`
* Make RKObjectRequestOperation cancel underlying request operation when cancelled

Code/Network/RKObjectManager.h

@@ -144,9 +144,6 @@ RKMappingResult, RKRequestDescriptor, RKResponseDescriptor;
  
  RestKit features deep integration with Apple's Core Data persistence framework. The object manager provides access to this integration by creating `RKManagedObjectRequestOperation` objects when an attempt is made to interact with a resource that has been mapped using an `RKEntityMapping`. To utilize the Core Data integration, the object manager must be provided with a fully configured `RKManagedObjectStore` object. The `RKManagedObjectStore` provides access to the `NSManagedObjectModel` and `NSManagedObjectContext` objects required to peform object mapping that targets a Core Data entity.
  
- Fetch Request Blocks ->> TODO
- Need to cover DELETE impacts...
- 
  Please see the documentation for `RKManagedObjectStore`, `RKEntityMapping`, and `RKManagedObjectRequestOperation` for in depth information about Core Data in RestKit.
  */
 @interface RKObjectManager : NSObject
@@ -396,7 +393,18 @@ RKMappingResult, RKRequestDescriptor, RKResponseDescriptor;
  @param objectRequestOperation The object request operation to be enqueued.
  */
 - (void)enqueueObjectRequestOperation:(RKObjectRequestOperation *)objectRequestOperation;
-// TODO: Need a cancel...
+
+/**
+ Cancels all operations in the object manager's operation queue whose requests match the specified HTTP method and path pattern.
+ 
+ Paths are matches against the `path` of the `NSURL` of the `NSURLRequest` of each `RKObjectRequestOperation` contained in the receiver's operation queue using a `RKPathMatcher` object.
+ 
+ @param method The HTTP method to match for the cancelled requests, such as `RKRequestMethodGET`, `RKRequestMethodPOST`, `RKRequestMethodPUT`, `RKRequestMethodPatch`, or `RKRequestMethodDELETE`. If `RKRequestMethodAny`, all object request operations with URLs matching the given path pattern will be cancelled.
+ @param pathPattern The pattern to match against the path of the request URL for executing object request operations considered for cancellation.
+ 
+ @see `RKPathMatcher`
+ */
+- (void)cancelAllObjectRequestOperationsWithMethod:(RKRequestMethod)method matchingPathPattern:(NSString *)pathPattern;
 
 ///-------------------------------------
 /// @name Making Object Requests by Path

Code/Network/RKObjectManager.m

@@ -28,6 +28,7 @@
 #import "RKMIMETypes.h"
 #import "RKLog.h"
 #import "RKMIMETypeSerialization.h"
+#import "RKPathMatcher.h"
 
 #if !__has_feature(objc_arc)
 #error RestKit must be built with ARC.
@@ -516,6 +517,22 @@ NSURL *RKBaseURLAssociatedWithURL(NSURL *URL)
     [self.operationQueue addOperation:objectRequestOperation];
 }
 
+- (void)cancelAllObjectRequestOperationsWithMethod:(RKRequestMethod)method matchingPathPattern:(NSString *)pathPattern
+{
+    NSString *methodName = RKStringFromRequestMethod(method);
+    RKPathMatcher *pathMatcher = [RKPathMatcher pathMatcherWithPattern:pathPattern];
+    for (NSOperation *operation in [self.operationQueue operations]) {
+        if (![operation isKindOfClass:[RKObjectRequestOperation class]]) {
+            continue;
+        }
+        
+        NSURLRequest *request = [(RKObjectRequestOperation *)operation request];
+        if ((!methodName || [methodName isEqualToString:[request HTTPMethod]]) && [pathMatcher matchesPath:[[request URL] path] tokenizeQueryStrings:NO parsedArguments:nil]) {
+            [operation cancel];
+        }
+    }
+}
+
 @end
 
 NSString *RKStringFromNetworkReachabilityStatus(AFNetworkReachabilityStatus networkReachabilityStatus)

Code/Network/RKObjectRequestOperation.m

@@ -192,6 +192,12 @@ static NSIndexSet *RKObjectRequestOperationAcceptableMIMETypes()
     return nil;
 }
 
+- (void)cancel
+{
+    [super cancel];
+    [self.requestOperation cancel];
+}
+
 - (void)main
 {
     if (self.isCancelled) return;
@@ -212,6 +218,8 @@ static NSIndexSet *RKObjectRequestOperationAcceptableMIMETypes()
         self.error = self.requestOperation.error;
         return;
     }
+    
+    if (self.isCancelled) return;
 
     // Map the response
     NSError *error;