#6203, #5935: variants of raise. 'reraise' is currently only inserted by the compiler when an handler does not catch the exception. The default 'raise' always start with a fresh backtrace.  There is also 'raise_nostack' which does not trigger the stack trace recording.  Bytecode only for now.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/raise_variants@14223 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02