Description:
------------
Creating a new DateTime object using a fixed string with a "GMT(+/-)nn" timezone (e.g. "GMT+12" or "GMT-10") results in the correct date and time being displayed, with but a badly formatted timezone ("GMT+1200", "GMT-1000")

(A note if the reader isn't aware... the Etc/GMT timezones actually perform the opposite of what they appear to be requesting.  GMT+12 is actually GMT minus 12 hours, and GMT-10 is actually GMT plus 10 hours)

The unix timestamp returned by this object is incorrect by 2*offset.  So, the GMT+12 returns a timestamp decremented 24 hours.  The GMT-10 returns a date/time incremented by 20 hours.

Creating a new DateTime object and passing in a DateTimeZone object using an Etc/GMT(+/-)nn (e.g.  "Etc/GMT+12") timezone displays timestamps and formatted timezone as expected.

Test script:
---------------
foreach (['Etc/GMT+12', 'Etc/GMT-10'] as $timezone) {
    $dTZ = new DateTimeZone($timezone);

    // Create a DateTime using the DateTimeZone object
    // This will display both formatted and unix timestamp as expected
    $dT = new DateTime('2013-12-13 18:49:00', $dTZ);
    echo $dT->format('Y-m-d H:i:s T'), PHP_EOL;
    echo $dT->getTimestamp(), PHP_EOL;


    // Create a DateTime using only a string representation
    // This will display the formatted date/time as expected, 
    // but with the incorrect timezone
    // The value returned by getTimestamp() for format('U') will
    // be off by 2*offset
    $dT2 = new DateTime($dT->format('Y-m-d H:i:s T'));
    echo $dT2->format('Y-m-d H:i:s T'), PHP_EOL;
    echo $dT2->getTimestamp(), PHP_EOL, PHP_EOL;
}

Expected result:
----------------
2013-12-13 18:49:00 GMT+12
1387003740
2013-12-13 18:49:00 GMT+12
1387003740

2013-12-13 18:49:00 GMT-10
1386924540
2013-12-13 18:49:00 GMT-10
1386924540


Actual result:
--------------
2013-12-13 18:49:00 GMT+12
1387003740
2013-12-13 18:49:00 GMT+1200
1386917340

2013-12-13 18:49:00 GMT-10
1386924540
2013-12-13 18:49:00 GMT-1000
1386996540