Throwing heap-allocated exceptions

[Richard Smith <richard@…>]

In four places in <boost/iostreams/device/mapped_file.hpp> heap-allocated exceptions are thrown, e.g.:

throw new BOOST_IOSTREAMS_FAILURE("invalid flags");

These should almost certainly be stack-allocated as elsewhere in Boost.IOStreams.

Patch attached.

[Daniel James]

(In [57602]) Allocate exceptions on the stack, not the heap. Refs #3612, by Richard Smith.

[Daniel James]

(In [58633]) Merge iostream fixes, mostly by Richard Smith.

Fixes #3612, #3311, #2094, #3010, #2894, #3011, #3352, #3505.