Wrt. threadlocal by default: shared module constructors

[Christopher Wright]

Brad Roberts wrote:
> An interesting side effect of these changes is that thread startup cost is 
> going to increase.  Yet more reasons to avoid globals and global 
> initialization.
> 
> -- Brad

It'll further promote use of threadpools. This isn't terribly safe 
because the globals for that thread are left in some arbitrary state -- 
yet more reason to avoid globals.