SAML2\Compat\Ssp\Logger->log is not compatible with PSR-3

[pradtke]

The PSR defined interface method public function log($level, $message, array $context = array()); takes a log level. PSR-3 defines the log levels as strings

https://github.com/php-fig/log/blob/3490ba5925e6dcbe6de950c5c6b8dce9f6e96eda/Psr/Log/LogLevel.php#L10-L17

The ssp compatibility logger uses a case statement with and compares them to the SSP const log levels with are ints. As a result there are no matches and nothing gets logged.

saml2/src/SAML2/Compat/Ssp/Logger.php

Lines 126 to 132 in b3a040e

	switch ($level) {
	case \SimpleSAML\Logger::ALERT:
	\SimpleSAML\Logger::alert($message);
	break;
	case \SimpleSAML\Logger::CRIT:
	\SimpleSAML\Logger::critical($message);
	break;

the log method should probably also handle the $context array in a similar fashion to the other methods.