[DOC beta] Move @private declaration to correct section.

YUIDoc expects the main documentation to be before any YUIDoc tags. If a
documentation block starts with `@private` the actual documentation will
be ignored, and only the method/property signature will be displayed.

Example before:

![screenshot](https://www.monosnap.com/image/p8SFHLweO2IhI2aEabdyWecMh.png)

Example after:

![screenshot](https://www.monosnap.com/image/1suooi03wXKnL2140YZn5ogTQ.png)
Merge pull request #4022 from rjackson/move_private_declaration

[DOC beta] Move @private declaration to correct section.