fix for noConflict to be applied

Currently when appling
````js
$.fn.bdatepicker = $.fn.datepicker.noConflict();
$('#dp3').bdatepicker();
````
there is error `TypeError: $.fn.datepicker is undefined` when merging defaults:
````js
opts = $.extend({}, $.fn.datepicker.defaults, locopts, elopts, options);
````
This pr solves it by using local variables.