allow for MySQL COMMENT field-attribute in Model attribute definition
revert the fail
the implementation for MySQL
Fixing 'identifier' being stored as the raw value of the 'id' rather than being wrapped in an object

Continuation of a fix outlined in [pull request 656](https://github.com/sequelize/sequelize/pull/656)
Spelling
Allow the omittion of values on autoincremental columns. Closes #673
Allow the datatype override for autogenerated relational keys
Comply with coding style
Comments for mysql + table comments
Update changelog
Merge branch 'comments'
Merge pull request #660 from echong/master

Fixing 'identifier' being stored as the raw value of the 'id' rather than being wrapped in an object
Merge pull request #673 from sevastos/value-omittion-of-autoincremental-numerics

BigInt/Datatypes enhancements
Updated changelog to reflect latest merge.