Add test that ensures allowNull

This commit adds a test that checks allowNull in combination with
primaryKey.
Fix increment and decrement usage with schemata
Apply allowNull even if column is a primaryKey
Merge pull request #2647 from qjroberts/increment-schemata-fix

Fix increment and decrement usage with schemata
fix(instance/attribute/field): an instance should not contain values per their field prop after create, fixes #2468
Merge branch 'master' of github.com:sequelize/sequelize
Merge pull request #2651 from sequelize/hotfix/primary-key-allow-null

Fix allowNull in combination with primaryKey
fix(test): dont use unsigned
Merge branch 'master' of github.com:sequelize/sequelize
remove node-sql and query generation syntactic sugar

This is an incomplete feature that seems to be unused by the user
base. Furthermore, it does not support incoming dialects (notably
MSSQL), and thus has been slated for removal for the 2.0 release
Merge pull request #2659 from mbroadst/remove-syntax-sugar

remove node-sql and query generation syntactic sugar