Description:
------------
base64_decode violates RFC 3548:

"Implementations MUST reject the encoding if it contains characters outside the base alphabet when interpreting base encoded data, unless the specification referring to this document explicitly states otherwise."

Reproduce code:
---------------
<?php
$strings = array(
                 'SW1wbGVtZW50YXRpb25zIE1VU1QgcmVqZWN0IHRoZSBlbmNvZGluZyBpZiBpdCBjb250YWlucyBjaGFyYWN0ZXJzIG91dHNpZGUgdGhlIGJhc2UgYWxwaGFiZXQu',
                 'SW1wbGVtZW$0YXRpb25zIE1VU1QgcmVqZWN0IHRoZSBlbmNvZGluZyBpZiBpdCBjb250YWlucyBjaGFyYWN0ZXJzIG91dHNpZGUgdGhlIGJhc2UgYWxwaGFiZXQu',
                 'SW1wbGVtZW0YXRpb25zIE1VU1QgcmVqZWN0IHRoZSBlbmNvZGluZyBpZiBpdCBjb250YWlucyBjaGFyYWN0ZXJzIG91dHNpZGUgdGhlIGJhc2UgYWxwaGFiZXQu'
                 );
foreach($strings as $string) {
  var_dump(base64_decode($string));
}
?>

Expected result:
----------------
string(93) "Implementations MUST reject the encoding if it contains characters outside the base alphabet."
bool(false)
string(92) "Implemem][??UTZXH[??[?Y??Z[??\X?\??]?YHH\?H[X]"





Actual result:
--------------
string(93) "Implementations MUST reject the encoding if it contains characters outside the base alphabet."
string(92) "Implemem][??UTZXH[??[?Y??Z[??\X?\??]?YHH\?H[X]"
string(92) "Implemem][??UTZXH[??[?Y??Z[??\X?\??]?YHH\?H[X]"