Fix (global) db leakage, by making db local.
Thanks to mickhansen for the fix.
Merge pull request #900 from xming/master

Fix (global) db leakage, by making db local.
Update changelog.md
Merge branch 'master' of https://github.com/sequelize/sequelize
add test case for `does not modify the passed arguments - count`
add test case for count `does not modify the passed arguments`