reverted pylibmc to 1.2.3 version

Reverted pylibmc to 1.2.3 version because django-heroku-memcacheify==0.5 require pylibmc==1.2.3 

https://github.com/rdegges/django-heroku-memcacheify/blob/master/setup.py#L18
Merge pull request #131 from luzfcb/patch-5

reverted pylibmc to 1.2.3 version