Fix case-sensitivity in discovery

Question

Fixes #133

该提问来源于开源项目：openid/php-openid

Answer 1

I needed this change to support my OpenID address I gladyly simplified the code to drop the mb_ereg_search_init part so now it's straightforward (see a3d0943).

About match array. I needed that change because otherwise match[0], used by the caller here:

        if (!preg_match_all($this->_link_find, $head_match[0],
                            $link_matches)) {
            ini_set( 'pcre.backtrack_limit', $old_btlimit );
            return array();
        }

Was getting a single character.

I guess it wasn't spotted before becuase basically preg_match was never used, and the mb_ereg_search return code was different...