Add tests for Utils.format (currently failing)
Fix bug in Utils.format that ignore falsy values.

Previously this would affect where clauses, e.g:
  User.findAll({ where: ['foo = ?', 0])
Would translate into:
  SELECT * FROM `Users`.`foo` = ?
Instead of:
  SELECT * FROM `Users`.`foo` = 0
Merge pull request #404 from watson/where-bug

Fix bug in Utils.format that ignore falsy values