PR#5957,PR#5920,PR#5925: LongString module to workaround 32bits string size limitations during bytecode linking (patch by Benoit Vaugon and Chet Murthy)

In PR#5925, Benoît Vaugon initially proposed the LongString module to
solve an issue with bytecode blocks of size > Sys.max_string_length on
32 bits architecture (16Mio). In PR#5957, Chet Murthy made small
changes to also fix the problem of debug information going above this
16Mio limit.

The LongString module should be reusable in other parts of the
compiler, should new 32bit-string-length issues arise.


git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13547 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02