Author: Rajesh Taneja
MDL-35047 tool_xmldb: Added missing strings for xmldb
http://git.moodle.org/gw?p=moodle.git;a=commit;h=08363c5c8078bd2f5fa863722acb1471293fe8a0
http://github.com/moodle/moodle/commit/08363c5c8078bd2f5fa863722acb1471293fe8a0
+ 2.3 en [duplicateindexname,tool_xmldb]
+ 2.3 en [indexnameempty,tool_xmldb]
+ 2.3 en [incorrectindexname,tool_xmldb]