Idp Initiated login tests + query param compatibility with shib

PSR2 / Whitespace

*    Updated the phpDoc comments to match the code
*    Added return statements
*    Added return values

#655 allow core:php to manipulate all of the state

Sorry, I broke it last night!

http_response_code() was introduced in 5.4 and that's our minimum now

Closes https://github.com/simplesamlphp/simplesamlphp/issues/962

It was deprecated in Twig 1.x and removed in 2.0.

This setting had to be an absolute path before.. This change is backwards compatible (absolute paths still work)

Use declared names of methods and classes