Datepicker bugfixing

[jmayday]

I removed code allowing values which do not match format being parsed as dates.

[antoinepairet]

@jmayday Could you squash the commits to make only one. Thanks in advance

[jmayday]

Squashed commits are available under branch https://github.com/jmayday/bootstrap/tree/datepicker-bugfixing-squashed and PR is here #3294

[jmayday]

I've had a look at antoinepairet@4d97d7c and it doesn't work so well with change I proposed (having call to new Date(viewValue) removed). Of course I don't mean that content of commit antoinepairet@4d97d7c is broken. It's good work actually. I would just like to clarify some working combination of these two fixes.

So, let's describe it this way:

• when my change is kept then date can't be initialized
• when my change is ignored (we keep calling new Date(viewValue)) then we still get values like "1" parsed into the model as date which is not necessarily expected

You can use this plunker to compare the behaviour - http://plnkr.co/edit/HKALJPWWnpyU8nU8iAvX

[wesleycho]

As mentioned in #2513, this fails some tests when based off of current master, and needs to be updated.

[chrisirhc]

Closing as #3294 is a newer version of this PR.