[Issue #963] Perform default handling for NSURLAuthenticationMethodDefault authentication challenges

Signed-off-by: Mattt Thompson <m@mattt.me>
Merge branch 'master' of github.com:AFNetworking/AFNetworking
[Issue #942] [Issue #943] Don't attempt to use URL-encoded credentials in connection:didReceiveAuthenticationChallenge:, since any included credentials would have to be invalid to have an authentication challenge be issued

Signed-off-by: Mattt Thompson <m@mattt.me>
Fixed a leak in requestWithMethod:path:parameters:

`CFStringConvertEncodingToIANACharSetName` is documented to follow CF’s create-rule, so the cast needed to be transferring ownership to ARC.
Merge pull request #989 from danyowdee/master

Fix for leaked strings in -[AFHTTPClient requestWithPath:method:params:]
Merge remote-tracking branch 'AFNetworking/master'

* AFNetworking/master:
  Fixed a leak in requestWithMethod:path:parameters:
  [Issue #942] [Issue #943] Don't attempt to use URL-encoded credentials in connection:didReceiveAuthenticationChallenge:, since any included credentials would have to be invalid to have an authentication challenge be issued
  [Issue #963] Perform default handling for NSURLAuthenticationMethodDefault authentication challenges