Fixes #2020 - Race Condition in UIImageView+AFNetworking when called twice with the same URL
Support NSSecureCoding in AFURLResponseSerialization
Support CGFLOAT_IS_DOUBLE  in AFImageResponseSerializer
[AFHTTPResponseSerializer] Use copy to ensure immutable types
Replace all uses of NSCoding to NSSecureCoding
Fix issue with downloadTaskDidFinishDownloading not being called

Set higher priority for [AFURLSessionManager downloadTaskDidFinishDownloading] and fallback to task delegate's implementation in case if session-level block returns nil or not implemented. Related to issue #2050.
Merge pull request #2021 from xonder/racecondition

Fixes #2020 - Race Condition in UIImageView+AFNetworking when called twi...
Don't update NSProgress for data tasks

1. Progress is never returned by data task methods, only download methods. Those methods update the progress elsewhere so removing this shouldn't affect them.
2. The totalUnitCount is never being set during data tasks, so even if it was being returned, the NSProgress always reports a fractionCompleted of 0 right now.
3. There is a crash that occurs here rarely. My best guess is that the delegate is still being sent messages as it's being released.
Merge pull request #2056 from pronebird/master

Fix issue with downloadTaskDidFinishDownloading not being called
[Issue #2046] Updating README about http session manager reachability
Merge pull request #2049 from kylef/securecoding

Support NSSecureCoding and CGFLOAT_IS_DOUBLE with response serialisers
Merge branch 'master' of github.com:AFNetworking/AFNetworking
Finishing transition from NSCoding to NSSecureCoding
Fixing mismatch property in extension
Adding @warning for -downloadTaskWithRequest:

Signed-off-by: Mattt Thompson <m@mattt.me>
[Issue #2053] Fix KVO leak on invalidated session tasks
Bumping version to 2.2.4