boost::bind() to pass any other coroutine arguments. This allows us to remove
the LLCoroBase and LLCoro constructs, directly storing a coroutine object in
our ptr_map. It also allows us to remove the multiple launch() overloads for
multiple arguments. Finally, it lets us move most launch() functionality into
a non-template method.

instances. LLCoros::launch() intends to address three issues:
- ownership of coroutine instance
- cleanup of coroutine instance when it terminates
- central place to twiddle MSVC optimizations to bypass DEV-32777 crash.
Initially coded on Mac; will address the third bullet on Windows.
Adapt listenerNameForCoro() to consult LLCoros::getName() if applicable.
Change LLLogin::Impl::connect() to use LLCoros::launch().
LLCoros::getName() relies on patch to boost::coroutines::coroutine::self to
introduce get_id().