Deglobalize default threshold value, and fix initialization of threshold variable.
Fix Refcounted docs - refCountedEnsureInitialized and refCountedIsInitialized did not exist.
Merge pull request #1379 from AndrejMitrovic/FixupRefcountDocs

[trivial] Fix Refcounted docs
Call thisTid to initialize first thread's message box, bypassing checks against setting thread-local variables from a shared static constructor.
Merge pull request #1369 from AndrejMitrovic/IsemailFix

Deglobalize default threshold value, and fix initialization of threshold variable
Merge pull request #1376 from yebblies/issue4923

initialize first thread's message box in a normal static ctor, to work around requirement that thread-local variables cannot be set from a shared static constructor.