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 19_STABLE

filter/tex/lib.php

@@ -3,12 +3,15 @@
 function tex_sanitize_formula($texexp) {
     /// Check $texexp against blacklist (whitelisting could be more complete but also harder to maintain)
     $tex_blacklist = array(
-        'include','def','command','loop','repeat','open','toks','output',
+        'include','command','loop','repeat','open','toks','output',
         'input','catcode','name','^^',
+        '\def','\edef','\gdef','\xdef',
         '\every','\errhelp','\errorstopmode','\scrollmode','\nonstopmode',
         '\batchmode','\read','\write','csname','\newhelp','\uppercase',
         '\lowercase','\relax','\aftergroup',
-        '\afterassignment','\expandafter','\noexpand','\special'
+        '\afterassignment','\expandafter','\noexpand','\special',
+        '\let', '\futurelet','\else','\fi','\chardef','\makeatletter','\afterground',
+        '\noexpand','\line','\mathcode','\item','\section','\mbox','\declarerobustcommand'
     );
 
     return  str_ireplace($tex_blacklist, 'forbiddenkeyword', $texexp);
@@ -34,4 +37,4 @@ function filter_tex_updatedcallback($name) {
     delete_records('cache_filters', 'filter', 'algebra');
 }
 
-?>
+?>