Revert "Fixing warning caused by default statement in switch statement that covered all enumeration values"

This reverts commit b5c48f13a1d42952da78ab3027b7d804048f525b.
Fix  [Issue #751]
Serialize calls to responseJSON using a lock.

AFJSONRequestOperation's completion path calls `responseJSON` from a
processing queue.  Because `responseJSON` "lazily" deserializes the
response data into a JSON object, it needs to be protected against
concurrent access from other queues (threads).

For example, `AFNetworkingOperationDidFinishNotification` is posted
when the operation finishes but perhaps before that processing queue
has finishing executing.  Notification observers who also access
`responseJSON` end up in a race with that queue that often leads to a
crash.

We reuse the existing lock from our AFURLConnectionOperation base
class.
[Issue #769] Resolving asymmetry in cached image case for UIImageView category
Updating OS X project settings
Merge pull request #768 from jparise/response-json-lock

Serialize calls to responseJSON using a lock.
Cleaning up formatting from pull request

Adding @dynamic for lock property
Merge branch 'master' of https://github.com/Fl0p/AFNetworking into Fl0p-master
[Issue #767] Consolidating macros
Wrapping AFHTTPBodyPart switch statement with #pragma to ignore -Wcovered-switch-default