The patch reimplements the core_string_manager::get_language_dependencies()
so that potentially mis-configured language packs with circular
dependencies or self dependency do not make the site unavailable.
Unit tests for the expected behaviour are added.
Includes:
* constants refactoring
* reworked db table init
* support for $CFG->debug = -1
* functional DB tests
* fixed $DB->get_indexes() to not throw exceptions when table does not exist
* fix handling of user passwords in test db
* add debug info to exception messages
* removed unnecessary PHP debug errors from mathslib
* fixed @error suppression in get_string
* fixed PHPUnit error handler setup
* added timezone info to default install
David Mudrák