SEC-2385: Document how to use with Spring 4
SEC-2425: Add Test for EnableGlobalMethodSecurity works on parent config
SEC-2386: Remove stack for AuthenticationManagerBuilder with no authenticationProviders
Fix typo in InternalAuthenticationServiceException javadoc
SEC-2367: ProviderManager rethrows InternalAuthenticationServiceExceptions
SEC-1932 Added PBKDF2PasswordEncoder.

 - Also moved some logic into a new class, AbstractPasswordEncoder. Both PBKDF2PasswordEncoder and the now-simplified StandardPasswordEncoder extend AbstractPasswordEncoder.
 - Added tests for PBKDF2PasswordEncoder .