Deadlock potential

[JssDWt]

The importScriptAddress function of ScopedKeyManager takes a Lock on ScopedKeyManager, then a Lock on Manager.

The Address function of Manager takes a RLock on Manager, then a RLock/Lock on ScopedKeyManager.

Combining the two can lead to a deadlock.

[JssDWt]

There's other occasions too where the locks of manager and scoped manager are reversed. A decision must be made:

• either always lock manager first, and then scoped manager
• or always lock scoped manager first and then manager

Probably manager first, then scoped manager makes most sense.
ImportPublicKey and importScriptAddress have this issue

[JssDWt]

We've been using this, apparently successfully, over the last few months:
breez@04ba108

Let me know if I should PR that.

[guggero]

Looks like a worthy PR, sure. Thanks for investigating in the first place!

[JssDWt]

Looks like a worthy PR, sure. Thanks for investigating in the first place!

#942