When opcache.validate_timestamps is disabled, then the new metadata will not be read after a metarefresh.
This can be solved by adding the metadata file to an opcache blacklist, but calling opcache_invalidate()
after writing a file is a nice out-of-the-box solution.

Hopefully, this will enable everybody that is using simplesamlphp to disable opcache.validate_timestamps
without running into problems.

To put it differently, to avoid OSX machines being identified as windows boxes, “darwin” should be evaluated *before* “win”.

Note that when normalising the directory separator, using
DIRECTORY_SEPARATOR causes tests to fail on non-Windows platforms
as its value is (correctly) "/".

Use InvalidArgumentException instead of SimpleSAML_Error_Exception when dealing with wrong input parameters.

SimpleSAML_Utilities::resolvePath was moved incorrectly to \SimpleSAML\Utils\HTTP instead of \SimpleSAML\Utils\System. Fix that.

Throw an exception on bad input parameters instead of using assert() in SimpleSAML_Utils_System::writeFile().

Schedule SimpleSAML_Utilities::writeFile() for removal.

Schedule SimpleSAML_Utilities::getTempDir() for removal.

Refactor SimpleSAML_Utilities::isWindowsOS() to SimpleSAML_Utilities::getOS(). Reimplemented to support most operating systems.

Schedule SimpleSAML_Utilities::isWindowsOS() for removal.