Description:
------------
To compile PHP with xmlreader, version >= 2.6.20 of libxml2 is required, otherwise the make will fail with an Unreferenced Symbol error for xmlTextReaderSchemaValidate (which was introduced in version 2.6.20).

This page:
http://au.php.net/manual/en/ref.libxml.php
says that version 2.6.0 is required. The actual xmlreader page:
http://au.php.net/manual/en/ref.xmlreader.php
doesn't specify a required version.

The Australian Mirror of xmlsoft doesn't have an up-to-date version of libxml2, so lots of people will hit this problem.

Reproduce code:
---------------
./configure --enable-xmlreader
gmake

Expected result:
----------------
A successful compile!

Actual result:
--------------
Undefined                       first referenced
 symbol                             in file
xmlTextReaderSchemaValidate         ext/xmlreader/.libs/php_xmlreader.o
ld: fatal: Symbol referencing errors. No output written to sapi/cli/php
collect2: ld returned 1 exit status
gmake: *** [sapi/cli/php] Error 1