Description:
------------
xml_get_current_byte_index is limited to 32-bit integers even on 64-bit builds, resulting in negative or incorrectly small results after parsing 2GiB or more XML text, which is well below PHP_INT_MAX.

To get the "Expected" results listed, I changed the definition on XML_GetCurrentByteIndex to be long instead of int, but I'm unsure if that's a truly portable fix.

Test script:
---------------
<?php
$parser = xml_parser_create('UTF-8');
xml_set_element_handler( $parser, 'startelement', null );

$emptylong = str_repeat(' ', 1024*1024);
xml_parse($parser, '<root><i></i><b/><ext>Hello</ext>', false);
for($i = 0; $i < 2896; $i++) {
    xml_parse($parser, $emptylong, false);
}
xml_parse($parser, '<ext></ext><ext></ext></root>', false);

function startelement($parser, $name, $attribute) {
    if ( $name == 'EXT' ) { echo "Byte Index:".xml_get_current_byte_index($parser)."\n"; }
}

Expected result:
----------------
Byte Index:21
Byte Index:3036676133
Byte Index:3036676144

Actual result:
--------------
Byte Index:21
Byte Index:-1258291163
Byte Index:-1258291152