Got rid of some compiler warnings because of const POD return values. I think it is unlikely that we will ever have return types that are modifiable as rvalue, so I think we can do without that const.
Merge branch 'master' of https://github.com/hmenke/espresso
Merge remote-tracking branch 'upstream/master'
Fixed a bug in observables when particle numbers are not contiguous.
fixed gpu implementation of [lbboundary delete]
Fixed correlation example, fixes to error messages
Merge pull request #157 from kosovan/master

Fixed correlation example, fixes to error messages
Merge branch 'master' of git://github.com/espressomd/espresso

Conflicts:
	src/tcl/statistics_observable_tcl.cpp
MMM1DGPU skeleton
Removed last traces of ignore_charges
Now also checking O3 if O5 is not possible (e.g. llvm)
particle print no longer checks for runtime errors, which cannot occur anyways
Removed the dysfunctional invalidate_system, updated checkpointing documentation.
Removed invalidate_system voodoo from tests
Updated NEWS.
Clarified docs on checkpointing.
Updated autotools files.
Missing cells_tcl.hpp
Merge branch 'master' of github.com:espressomd/espresso
Add derived features to code_info.