extras/slaveactivity: fix potential segfault if no master activity is set

Signed-off-by: Ruben Smits <ruben.smits@intermodalics.eu>
cmake: add all standard rpaths for all kind of targets to all kind of targes

Since the rpath_use_link_paths cmake option does not work on OSX with cmake < 3.0 this is a way to make sure that in-project targets can link with eachother.

Signed-off-by: Ruben Smits <ruben.smits@intermodalics.eu>
Merge remote-tracking branch 'upstream/slave_activity_fix' into next
Merge remote-tracking branch 'upstream/rpath-mess' into next