PHPTests for the DOMDocument::load and DOMDocument::loadXML

The tests cover the following cases for both methods:
- The basic behavior
- The use of the libxml options: LIBXML_DTDATTR, LIBXML_NOCDATA, LIBXML_NOENT, LIBXML_NOBLANKS, LIBXML_NOERROR, LIBXML_DTDVALID, LIBXML_DTDLOAD
- The following not-well formed xml cases:
  - Extra content at the end of the doc
  - Wrong xml version
  - Typo in the tag name
  - Attribute value withot quotation marks
  - Opening and ending tag mismatch