Do not yield back to taskmanager in spinlock

[davetcc]

Yielding back to taskmgr in this situation is a recipe to deadlock the bus, as at some point two things get held up waiting for the same lock, and neither can acquire.

Locks are designed for things that are fleeting in scope, IE to control access to shared state for a few microseconds, not for things that last long enough to need yielding.

[davetcc]

reference docs updated to include a warning that yieldForMicros must never be called within a lock.

[davetcc]

This is now valid, I'll update all documentation over the next day or so to match our finds of how it works in heavy use