Avoid calling SimpleSAML_Utilities::normalizeURL() twice when we are redirecting and need to check if the URL is trusted.
Remove extra URL validation as normalizeURL() will have done that already. Return an empty string if the input URL is empty (disregarding its type). This should make the checkURLAllowed() function transparent and avoid it returning the current URL (normalized) when input is empty. Fixes #99.
Add / fix assertions for the redirect*() functions in SimpleSAML_Utilities.
Reformat documentation of the redirect*() functions in SimpleSAML_Utilities.