* default setting is to use one thead
* multiple threads can be set using the lzma options
* old behavior can be forced by defining BOOST_IOSTREAMS_LZMA_NO_MULTITHREADED
Needs lzma.jam file in tools/build module.
See also trac ticket 7534.
The code has been around in random places since some time,
I only added tests and build system updates and
minor fixes for issues those tests discovered.