First pass at NSURLSession-esque auth challenges
Internally switch CKUploader over to new auth challenge delegate method
Switch CKUploader's API over to modern auth handling
Redclare old auth challenge delegate message, but as deprecated
Internally switch CK2OpenPanel to modern auth API
Update open panel's API to modern convention
Correct selector used for open panel auth
Switch to using a block instead of CK2AuthenticationChallengeTrampoline

MASSIVELY simpler!
Protect against clients accidentally calling auth completion handler more than once
Scooch 32/64 bit build setting up to project level

Shuts up Xcode's warning for me. Maybe other people still see it? I'm
worried this won't work out once we support iOS
Shift release of panel at end of sheet to a different spot
Avoids a crash should someone call, say, -cancel: for a second time
Merge branch 'v2.x-beta' into auth-block
Use native protection space rejection when possible
Use native -performDefaultHandlingForAuthenticationChallenge: routine when possible
Better description and domain for DAVKit errors
Leave 405 errors unedited for now as can happen during more than writes
Generate error descriptions appropriate to the file operation
Generate passable description when accessing root folder fails
Merge branch 'v2.x-beta' into auth-block
Make a stab at handling cancellation mid host key challenge