mod/hotpot MDL-22726 fix importing of intructions from a Hot Potatoes quiz file into the Moodle question bank

ensure user has_capability('mod/hotpot:attempt', $module) when viewing a HotPot or submitting results

MDL-19718 fixed critical race condition when deleting posts - credit goes to Ashley Holman; backported from MOODLE_19_STABLE

stricter checking of null fields when restoring HotPots in order to avoid unwanted chars being inserted into empty char fields on PostgreSQL sites

 from HEAD

MDL-20184 more efficient and accurate detection of missing nodes in xml tree when importing Hot Potatoes XML files to Moodle question bank / quiz module

MDL-20184 when importing questions from Hot Potatoes files to Moodle question-bank / Quiz module, the readquestions() function wil return "false", to signify an error, if no questions are detected in the import file

MDL-20185 detect zero, "0", as an answer for a gap in a JCloze when importing to the Moodle's question bank / Quiz module

HotPot module: differentiate between "guesses-correct" (JCloze) and "guess-correct" (JCross, JMatch, JMix, JQuiz) in HotPot xml files and fix PreloadImages function for multiple images

add hotpot_encode_content_links() and hotpot_decode_content_links() to HotPot's backuplib.php and restorelib.php respectively

MDL-19842 securing algebradebug the same way as text debug - only admins may use it now; backported from HEAD

fixes for XHTML strict: add <fieldset> arround hidden form fields, use "id" instead of "name" to locate forms, use HTML entities in button captions <= and =>

when searhcing for urls of next quiz, remove requirement for navigation buttons to have class="NavButton"

MDL-18893 TeX filter - fine tune "def" commands + add some more commands to blacklist (from Kopete).
Thanks to Mauno Korpelainen and Steve Mayer. Backported from 18_STABLE

MDL-18384 better symlink support, do not recurse symlinks when deleting - patch by Matt Oquist, thanks; backported from MOODLE_19_STABLE

when search for media players, remove requirment for <object> tag to contain a space, and make closing </A> tag lowercase