hacker's fix of the memory problem when creating photon tracks. This is not properly tested, yet.

(cherry picked from commit 99afcadd11ab71d6f37da629ffe46f908e1570fe)
debugging and suppressing poisson distribution for single-photon flashs.

(cherry picked from commit f3d82bcb2a18878b4a661f7fbd91db7e8d11af7d)
auto reformat propagation kernel using the clang-format tool.

no actual changes have been made in this commit.
hole ice: beginning to implement cylinder

(on the basis of commit f20a465661b054dab97c5192d7c2af0c2bf461af)
Merge branch 'sf/hole-ice' into sf/switches