avoid to delete __init__.py so that make after make clean does not fail
added rdf as core observable so that it can be used for averaging
Merge branch 'master' of https://github.com/espressomd/espresso

Conflicts:
	src/python/espressomd/Makefile.am
Merge branch 'master' of https://github.com/espressomd/espresso
Merge branch 'master' of https://github.com/espressomd/espresso
Merge branch 'master' of https://github.com/espressomd/espresso
Merge branch 'master' of https://github.com/espressomd/espresso
fixed observable structure_factor
added fast implementation of structure factore for the use with correlater
fixed formatted output of structure factor
fixed typo
removed check that observable is not unnecessarily updated
Merge pull request #196 from dschwoerer/master

new observables