Fix documentation for appendPartWithFileURL:name:error:.

The documentation said that the values for filename and the
Content-Type header was being obtained from a NSURLResponse,
but since this is a request, no response is available yet.

The documentation has been changed to reflect better where
those values really come from.
Add method to allow custom file name and content type for multiparts.

The previous method was selecting the file name and the MIME type
automatically depending on the given file URL.

The new method allows specifying a custom file name and a custom
MIME type for the those parts.
Add asterisk (*) as a percent escaped character since it's in the reserved words per the RFC
The documentations states registered operation classes are consulted to the reverse order in which they are registered. New registrations are added to the beginning of the array in the register implementation. Fixed using the reverseObjectEnumerator when iterating the array which produced the opposite of documented behaviour. fixes #794
changed op_class variable to more objective-c style variable name operationClass
Merge pull request #849 from joelparsons/master

AFHTTPClient Registered operation classes consulted in wrong order.
Merge pull request #806 from drodriguez/gh-800-multipart-custom-filename

Add parts with custom file names and MIME types
Minor formatting fix
Minor formatting fixes
Merge pull request #844 from karbonworks/master

Add asterisk (*) as a percent escaped character...
UIImageView+AFNetworking not using setHTTPShouldHandleCookies

Signed-off-by: Mattt Thompson <m@mattt.me>
added properties keeping reference to success block and failure block
Merge remote-tracking branch 'AFNetworking/master'

* AFNetworking/master:
  UIImageView+AFNetworking not using setHTTPShouldHandleCookies
  Minor formatting fixes
  Minor formatting fix
  changed op_class variable to more objective-c style variable name operationClass
  The documentations states registered operation classes are consulted to the reverse order in which they are registered. New registrations are added to the beginning of the array in the register implementation. Fixed using the reverseObjectEnumerator when iterating the array which produced the opposite of documented behaviour. fixes #794
  Add asterisk (*) as a percent escaped character since it's in the reserved words per the RFC
  Add method to allow custom file name and content type for multiparts.
  Fix documentation for appendPartWithFileURL:name:error:.