Description:
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More info: http://news.php.net/php.internals/64147

I ended up digging deeper and created a patch for this.

Summary of changes:
- Created a new tz_checked_valid flag on the global date structure
- Created a callback method when date.timezone is modified by the ini (set)
- Callback checks validity if set during runtime, and will error (with line number) accordingly. This is probably useful for some users that might no otherwise have realized they made a mistake on their ini_set() line in their code.
- In guess_timezone(), if tz_checked_valid is not set, attempts to validate, errors if cannot.

As previously noted from my benchmarks, over 1 million runs, it increased performance from:
date                    : 1.751 sec
strftime                : 1.872 sec
strtotime               : 3.195 sec

to:
date                    : 1.238 sec
strftime                : 0.999 sec
strtotime               : 2.337 sec

Here is a test case to show that it will not blow up on invalid timezones, and revalidates accordingly:

<?php
ini_set('date.timezone', 'FAKE_TIMEZONE');
echo date('F j, Y, g:i a');

ini_set('date.timezone', 'America/Chicago');
echo date('F j, Y, g:i a');
?>

Note: If the ini is actually set wrong, it will not error until they call a date function that makes use of the timezone, just like before.

Thanks!

Test script:
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$c = 1000000;
for($i=0; $i<$c; $i++) date('F j, Y, g:i a');

etc..

Expected result:
----------------
Performance results are benchmarked and displayed in the general description

Actual result:
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Performance results are benchmarked and displayed in the general description