Autosave bug fix, updated color field, select standardizing

* Fixed autosave bug that prevented fields to be updated in a normal post save
* `color` field in WordPress 3.5 installs now take advantage of the built in color picker (See https://github.com/rilwis/meta-box/issues/257)
* The `std` argument is now used to set the default option of a `select` field (See https://github.com/rilwis/meta-box/issues/254).  Demo file changed accordingly