meet the AR interface requirements.

now supports mapped primary key when _id is part of source with an
alias.

strict sql dbms like postgres would fail otherwise

this allows us to implement other activerecord implementations based on
NoSQL dbms

Control statements based on the if and elseif constructs must have a single space before the opening parenthesis of the conditional and a single space after the closing parenthesis.

fixes #1072

Finished ActiveDataProvider.