Merge pull request #228 from joergkappes/master

Fix problems when downloading external source
Nesterov algorithm added. The caller is pending
smoothing strategy added
Only link against librt if on Linux, not on Apple or Windows.
minor bug fixes
Merge pull request #234 from joergkappes/master

add missing include cmath in visitors.hxx
Merge pull request #233 from chaubold/fix/combilp_mac

Only link against librt if on Linux, not on Apple or Windows.
Merge pull request #232 from homul/master

Nesterov algorithm added. Caller for it is still pending
Merge pull request #62 from opengm/master

update from opengm:master