Description:
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Found an example of a valid tgz file which is a valid tar file, but complains about an invalid checksum.

It extracts with `tar -xvzf /tmp/foo.tgz` and also extracts fine from 7zip.

I have also tried decompressing it before using `PharData` and it still fails which means it's not the decompression doing it.

Test script:
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<?php

$download = 'http://thrysoee.dk/editline/libedit-20100424-3.0.tar.gz';
$file = '/tmp/libedit20100424.tgz';

file_put_contents($file, fopen($download, 'r'));
var_dump(new PharData($file));

Expected result:
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To see the PharData object in the console.

Actual result:
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PHP Fatal error:  Uncaught UnexpectedValueException: phar error: "/tmp/libedit20100424.tgz" is a corrupted tar file (checksum mismatch of file "libedit-20100424-3.0") in /tmp/phpbugtest2.php:7
Stack trace:
#0 /tmp/phpbugtest2.php(7): PharData->__construct('/tmp/libedit201...')
#1 {main}
  thrown in /tmp/phpbugtest2.php on line 7