[Boost-build] threading=single should be prohibited under MSVC-8.0

From: Andrei Melnikov (andy.melnikov_at_[hidden])
Date: 2006-08-09 20:15:37

bjam runtime-link=shared/link=shared/variant=release produces two
identical dlls instead of just one:

boost_date_time-vc80-mt-1_35.dll
boost_date_time-vc80-1_35.dll

The second DLL is built using
runtime-link=shared/link=shared/variant=release/threading=single. It
is useless because:

1) It is never used by autolinking
2) The command lines for the two libraries are the same.

I think BBv2 shouldn't build this variant by default, just like
link=dynamic/runtime-link=static under Linux. And should print an
error if threading=single is set explicitly on the command line or in
the build properties.
-- 
Andrei