Also make the default namespace parameter mandatory, so that the function is not ADFS-specific.

To convert existing tests to use the base class use

 perl -p -i -e 's/PHPUnit_Framework_TestCase/SimpleSAML\\Test\\Utils\\ClearStateTestCase/g' `grep -rl PHPUnit_Framework_TestCase tests | grep -v ClearStateTestCase.php`

A PHPUnit listener unsets SSP environmental variables and attempts
to restore globals.

Accessing a key in an array is not allowed when the array is not a variable but a value returned by a function.

This also required adding an additional argument to
SimpleSAML\Utils\Crypto::loadPrivateKey to ease in testing. Without
this additional argument, SimpleSAML_Configuration::getBaseDir eventually
gets called to determine the private key location.  This doesn't work
well with vfsstream. This argument shouldn't cause too much trouble, and
seems cohesive enough with the function's purpose.

Formatting, namespaces, phpdoc.

This enables too the implementation of additional contact attributes, as requested in #509 to support the SIRTFI framework.

This resolves #476.