Associated to multisite loading & context stuff. I choose to commit this
change in master because it is important to not break the fact that
the buildconf HAS TO be importable safely outside any context.

Adds a LODEL2LOGDIR to buildconf.py
Adds a nginx-conf option to slim
...

It a real buildtime variable, the localestatedir

Using $pkgpythondir instead of $pythondir in Makefile.am
Solves a bug that put installed files in site-packages instead of dist-packages on debian

IMPORTANT : tests are broken. See details below

A new lodel/buildconf.py.ini file created. It will be transformed to a lodel/buildconf.py file by ./configure .
This file goal is to store build time constant (for the moment the presence of pymongo).
You have to build lodel2 before being able to run the tests.