Allow dots in Observe keys

[daffl]

I already merged this fix into the 1.2 develop branch with #309 but suggest to make this part of the 1.1.5 release as well. All tests are still passing and it doesn't introduce a new API. The fix makes this possible:

var ob = new can.Observe();

ob.attr('a.b', 'test');
ob.attr() // -> { a: { b: 'test' } }

ob.attr({
    'a.b': 'test'
});

ob.attr() // -> { 'a.b': 'test' }

ob.attr('a.b')
// will look for 'a.b' first
// and then for ob.attr('a').attr('b')

Since new Observe({ 'test.key': 'value' }) failed before, introducing the direct key lookup for obsreve.attr('test.key') (and falling back to the nested property lookup if it doesnt' exist) shouldn't pose a problem for any existing functionality. Fixes #257 and #296.

[schovi]

Having issue with set dotted key

Your example

var ob = new can.Observe();

ob.attr('a.b', 'test');
ob.attr() // -> { a: { b: 'test' } }

Throw me classic old error "can.Observe: Object does not exist"

http://jsfiddle.net/schovi/zTF9s/

Read works fine