refactor social security code

Change SocialAuthenticationFilter to extend
AbstractAuthenticationProcessingFilter,
and override unsuccessfulAuthentication to handle redirect exception;
Change SocialAuthenticationRedirectException to extend
AuthenticationException;
Add Connection<?> to SocialAuthenticationToken;
Update unit test;
fix unit test and bugs
fix bug in SocialAuthenticationFilter
Fixed NPE caused when returning null for boolean
Unified new social/security signin with original ProviderSignInController code by reusing ProviderSignInAttempt instead of SignInAttempts.
Polish
Polish
Merge branch 'master' of github.com:habuma/spring-social
Merge pull request #78 from habuma/master

Merged Spring Security integration work (work in progress)