Author: David Monllao
MDL-55287 search: Custom error message if solr extension is not installed
Correcting engine is not installed lang string as well.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=e240a6132ddd59aee283533cd8dd4cce283d39ed
http://github.com/moodle/moodle/commit/e240a6132ddd59aee283533cd8dd4cce283d39ed
+ 3.2 en [enginenotinstalled,core_search]