[boost] [threads] namespace & externs

Boosters, In boost/thread/src/pthread/thread.cpp we see extern "C" {} around code such as tls_destructor. Is this needed so it interfaces w/ native pthread local storage? When a vendor program is built against a specific version of boost it usually becomes necessary to isolate other users via a namespace. However, anything with extern "C" style defeats this. Aside from explicit linking to native c api's are there reasons for this; also what's considered the best style to isolate different versions -- currently we modify every header with a version-ed namespace wrapper. thanks! -s-