Compare NSURLRequest rather than NSURL

If you inadvertently load a nil URL in UIImageView+AFNetworking, the failure block of the image request operation is bypassed because [nil isEqual:nil] == NO. By comparing the URL request instead of the URL, the `isEqual:` test passes and the error is properly forwarded to the failure block parameter.
Adding lock around AFHTTPRequestOperation -responseString
Adding lock around AFURLConnectionOperation -responseStringEncoding

Adding check for self.response in AFURLConnectionOperation -responseStringEncoding
Merge pull request #772 from 0xced/fix-uiimageview-nil-url

Compare NSURLRequest rather than NSURL
Fixing warnings caused by implicit property attributes
Ignoring -Wcovered-switch-default in AFHTTPBodyPart -hasBytesAvailable
Merge branch 'master' of github.com:AFNetworking/AFNetworking
Using DISPATCH_QUEUE_CONCURRENT for all calls to dispatch_queue_create for media type processing queues
Use dispatch_once to initialize content-type-specific processing queues

Signed-off-by: Mattt Thompson <m@mattt.me>
Added support for repeated key value pairs through use of NSSet
Merge pull request #778 from Neonkoala/master

Support for repeated key value pairs in URL encoded forms
Fixed comment typo

Minor typo.
Merge pull request #786 from tewha/patch-9

Fixed comment typo
Ensure content type for path extension doesn't return null
Merge pull request #792 from zachwaugh/master

Fix content type for extension from returning null
[Issue #791] Matching operations on request URL path rather than absolute URL string
Merge branch 'master' of github.com:AFNetworking/AFNetworking
Adding comma (,) as a percent escaped character since it's in the reserved words per the RFC
Fixes -[AFURLConnectionOperation totalBytesRead] threading issue.
Merge pull request #825 from OliverLetterer/thread-issue

Fixes -[AFURLConnectionOperation totalBytesRead] threading issue.