compile fix
fix release build warning
flags for various compilers

easier compilation with different compilers

- clang 3.5 on linux
- default to intel compiler if available
- default to native CPU for gcc
- openmp also for C
- compile for native CPU on os x
- try to make it compile with gcc 4.8 on os x
fix icc warning
stopwatch class
vassert macro

graceful termination of single MPI process after failed assertion
cooperate better with vassert
embree based ray caster for remote hybrid rendering
allow for delayed connection to vistle