Description:
------------
When ever date.timezone INI setting or date_default_timezone_set() is used and a clearly invalid timezone ID is set, DateTime::getLastErrors() has no indication of this.  Same if no timezone is set.

Test script:
---------------
// assume date.timezone currently set to "America/Los_Angeles" for this test
date_default_timezone_set( "asdf" );
try {
	$d = new DateTime();
}
catch ( Exception $ex ) {
	var_dump( DateTime::getLastErrors() ); // never even reached - $d is actually valid and set to "America/Los_Angeles" timezone, and DateTime::getLastErrors() has no errors listed
}

ini_set( "date.timezone",  "asdf" );
try {
	$d = new DateTime();
}
catch ( Exception $ex ) {
	var_dump( DateTime::getLastErrors() ); // reached, but no errors listed here
}

Expected result:
----------------
DateTime::getLastErrors() always contains the "The timezone could not be found in the database" error if a bad timezone name is preset, or "You are *required* to use the date.timezone setting or the date_default_timezone_set() function" error if no timezone name is preset.

Actual result:
--------------
DateTime::getLastErrors() contains no such errors or warnings.