* nickvergessen/ticket/10942:
[ticket/10942] Avoid possible conflicts with magic words in unit tests
[ticket/10942] Add access modifiers
[ticket/10942] Use ANSI SQL standard || in dbal.php
[ticket/10942] Fix up unit tests for sql_case()
[ticket/10942] Require same data type and do not cast expressions automatically
[ticket/10942] Make unit tests for sql_case simpler
[ticket/10942] Add a comment why we cast to sql_case()
[ticket/10942] Rename method sql_conditional() to sql_case()
[ticket/10942] Change term string to expression to avoid confusion
[ticket/10942] Fix sql_conditional for mssql, postgre and oracle
[ticket/10942] Fix function name on order_lower_test.php
[ticket/10942] Add unit tests for sql_concatenate
[ticket/10942] Add sql_concatenate to dbal
[ticket/10942] Add unit tests for sql_conditional
[ticket/10942] Add sql_conditional to dbal