Support to elasticsearch using the evelopment version of haystack

I needed to use elasticsearch but django-haystack in its 1.7.2 doesn't support it.  Just the 2.x beta.

I did some modifications to install this beta version of django-haystack and a few migration steps on search_indexes.py. Also the settings of the demo_project.

It has backwards compability if anyone prefers to continue using the haystack 1.7.2