Add basic function and trigger migrations

Added the ability to define migrations that create, drop, and rename
both functions and triggers (since triggers need functions).  This
allows migrations to handle more of the requirements of setting up
the underlying SQL database behavior.

This version currently only provides support on postgresql.
Merge remote-tracking branch 'upstream/master' into basic_function_and_trigger_migrations
Initial commit for join table model
insert into join table
Initial commit for join table model
insert into join table
Merge head
Support for getting join table model data
alias the queryinterface on hasmany double linked for brevity
Create an alias for connectorDAO for brevity
slight variable renaming
Custom event emitter uses setImmediate over process.nextTick if supported. Closes https://github.com/sequelize/sequelize/issues/869
Forgot to move the tick variable to the top of the file in custom event emitters.
Initial commit for hooks.. need to stash this for another PR
Adds hooks / callbacks / lifecycle events

This commit adds the ability of hooks for the DAOFactory. The following
hooks (in their order of operations) are:

(1) beforeValidate(dao, fn)

(-) validate

(2) afterValidate(dao, fn)

(3) beforeBulkCreate(daos, fields, fn)
    beforeBulkDestroy(daos, fields, fn)
    beforeBulkUpdate(daos, fields, fn)

(4) beforeCreate(dao, fn)
    beforeDestroy(dao, fn)
    beforeUpdate(dao, fn)

(-) create / destroy / update

(5) afterCreate(dao, fn)
    aftreDestroy(dao, fn)
    afterUpdate(dao, fn)

(6) afterBulkCreate(daos, fields, fn)
    afterBulkDestory(daos, fields, fn)
    afterBulkUpdate(daos, fields, fn)

There's a new file called hooks.js which works very similar to
mixins.js which just extends a prototype.

You can add the hooks like so...

... via .define():

var User = sequelize.define('User', {
  username: DataTypes.STRING,
  mood: {
    type: DataTypes.ENUM,
    values: ['happy', 'sad', 'neutral']
  }
}, {
  hooks: {
    beforeValidate: function(user, fn) {
      user.mood = 'happy'
      fn(null, user)
    },
    afterValidate: function(user, fn) {
      user.username = 'Toni'
      fn(null, user)
    }
  }
})

... via .hook() method

var User = sequelize.define('User', {
  username: DataTypes.STRING,
  mood: {
    type: DataTypes.ENUM,
    values: ['happy', 'sad', 'neutral']
  }
})

User.hook('beforeValidate', function(user, fn) {
  user.mood = 'happy'
  fn(null, user)
})

User.hook('afterValidate', function(user, fn) {
  user.username = 'Toni'
  fn(null, user)
})

... via direct method:

var User = sequelize.define('User', {
  username: DataTypes.STRING,
  mood: {
    type: DataTypes.ENUM,
    values: ['happy', 'sad', 'neutral']
  }
})

User.beforeValidate(function(user, fn) {
  user.mood = 'happy'
  fn(null, user)
})

User.afterValidate(function(user, fn) {
  user.username = 'Toni'
  fn(null, user)
})

Quick example:

User.beforeCreate(function(user, fn) {
  if (user.accessLevel > 10 && user.username !== "Boss") {
    return fn("You can't grant this user that level!")
  }

  return fn()
})

User.create({
  username: 'Not a Boss',
  accessLevel: 20
}).error(function(err) {
  console.log(err) // You can't grant this user that level!
})

As of right now, each hook will process in the order they where
implemented / added to the factory.

To invoke the hooks simply run...

Model.runHooks.call(Model.options.hooks.<hook>, <args>, <callback>)

Some model hooks have two or three paramters sent to each hook
depending on it's type.

Model.beforeBulkCreate(function(records, fields, fn) {
  // records = the first argument sent to .bulkCreate
  // fields = the second argument sent to .bulkCreate
})

Model.bulkCreate([
  {username: 'Toni'}, // part of records argument
  {username: 'Tobi'} // part of records argument
], ['username'] /* part of fields argument */)

Model.beforeBulkUpdate(function(attributes, where, fn) {
  // attributes = first argument sent to Model.update
  // where = second argument sent to Model.update
})

Model.update(
  {gender: 'Male'} /*attribures argument*/,
  {username: 'Tom'} /*where argument*/
)

Model.beforeBulkDestroy(function(whereClause, fn) {
  // whereClause = first argument sent to Model.destroy
})

Model.destroy({username: 'Tom'} /*whereClause argument*/)

For 1.7.x backwards compatibility, I've added a new method called
.hookValidate() since .validate() is a synchronous function. All of
Sequelize's API functions will invoke .hookValidate(), but if you
utilize the .validate() function outside of Sequelize then you'll
need to update your code if you want to run before/afterValidate hooks.

Sequelzie 2.0.x will not need this change simply because it's
.validate() method is already asynchronous. However, it will have the
.hookValdate() function in order to make the transition from 1.7 to 2.0
smoother and easier. Eventually we'll want to deprecate this function.

In addition to this commit, I've also completed the following tasks:

Move validation of enum attribute value to validate method

I had to complete that task in order to get the validate hooks
working properly.

And the last thing, I fixed executables.test.js if your DB didn't use
the default values for config/config.js, this was causing errors for me
on my local machine.
Merged master and forgot to Object.keys() for skipping validations.
Fixed a small hooks undefined problem.
Don't delete the pk of join table model
remove any previously defined pks in join table model
Unit tests for function and trigger migrations