Updated backtrace patch

I’ve updated my backtrace patch to work with OCaml 3.11.x as well as 3.10.x. The patch provides

• access to backtraces from within a program (this is already provided in stock 3.11.x)

• backtraces for dynamically-loaded bytecode

• backtraces in the (bytecode) toplevel

In addition there are a few improvements since the last version:

• debugging events are allocated outside the heap, so memory use should be better with forking (on Linux at least, the data is shared on copy-on-write pages but the first GC causes the pages be copied)

• fixed a bug that could cause spurious “unknown location” lines in the backtrace

• a script to apply the patch (instead of the previous multi-step manual process)

See ocaml-backtrace-patch on Github or download the tarball.