Execution of installed binary broken for Geant4.10.4 onwards

[Laurie Nevay]

When compiling geant4.10.4 onwards, the bdsim executable cannot be executed from the install dir.

LN-MacBook:~ nevay$ bdsim --help
dyld: Library not loaded: @rpath/libG4Tree.dylib
  Referenced from: /Users/nevay/physics/reps/bdsim-develop-install/bin/bdsim
  Reason: image not found
Trace/BPT trap: 5

[Laurie Nevay]

Add rpath to installation executables so they can correctly load dylibs (ie execute at all) without LD_LIBRARY_PATH being set for geant4. Fix Issue #232.

→ <<cset a04385db1c1d>>