Merge pull request #15 from praeclarum/master

Preserve cookies in WebAuthenticators and better Redirect URL detection
Revert "Merge pull request #15 from praeclarum/master"

This reverts commit 339abae05b64d60aec83b06275da55eac0f99822, reversing
changes made to b839665176c64659a84442a6f3567e98a61d19a8.

The new API to restore cookies is rather redundant, since if you already
have an Account, you'd use it to make requests instead of authorizing
again.
Restore early redirect detection changes
Add ClearCookiesBeforeLogin and ClearCookies()

The general assumption is that the user is showing the login UI to login a
new user. With that, automatically clearing the cookies before showing the
UI works to ensure they're not getting logged back into the user they're
already logged in as when switching accounts.

However, in situations where XA is only half of the story (like Azure
Mobile Services), it's useful to just keep the cookies but have a way to
clear them manually. So, in order to maintain current behavior,
ClearCookiesBeforeLogin was added and defaulted to true.
Make ClearCookies() static
FormAuthenticatorFieldType should X_AUTH_INTERNAL
[iOS] Propagate errors properly (fixes #13)
Bump Version
Use TaskCompletionSource instead of Task.Factory.StartNew where simple result is needed
Merge pull request #22 from stampsy/xamarin-pr-avoid-starting-tasks-where-possible

Use TaskCompletionSource instead of Task.Factory.StartNew where simple result is needed
Preserve synchronization context because OnRetrievedAccountProperties uses it
Propagate GetAccessTokenAsync exceptions to the calling code
Expose RequestAccessTokenAsync down the hierarchy (Google can use it to obtain access tokens with refresh_tokens)
Make authorization header generation overridable. We need this to implement Twitter Reverse Auth. Licensed under MIT/X11
Add GetValueFromJson to WebEx

This function was previously defined in FacebookService inside Xamarin.Social,
but we also needed it for implementing GoogleService, so it makes sense
to make it available as a help method in WebEx, which is shared by both Auth and Social.

Commit licensed under MIT/X11
Update iOS csproj targets
Don't block threadpool threads waiting for request

Resolves #23
Merge pull request #24 from stampsy/xamarin-pr-preserve-synchronization-context

Preserve synchronization context because OnRetrievedAccountProperties uses it
Merge pull request #29 from stampsy/xamarin-pr-expose-requestaccesstokenasync

Expose RequestAccessTokenAsync down the hierarchy
Merge pull request #30 from stampsy/xamarin-pr-make-oauth1-header-configurable

Make OAuth 1 header generation overridable