Support a mechanism for modules to execute code in Daemon thread

Currently, if a module wants to execute code with elevated privileges, it needs to either use proxy privileges, or else store a username and password and use those to authenticate. This leads to ugly code and/or security flaws.

Instead, we need a mechanism for a module to run code within a Daemon thread that has the appropriate privileges for the module (at first this will always be super user privileges, but in the future, Daemon can impose tighter control).

Proposed solution:

1. When the module framework starts/refreshes a module, it should create a secure token for each module, look for a method on each module's activator like

   void setDaemonToken(DaemonToken)

   . If present, we inject the daemon token for the module.

2. Add methods like the following, which throw an exception if you don't pass back exactly the token that the module architecture gave you:

   Thread Daemon.executeInDaemonThread(Runnable, DaemonToken)
   void Daemon.executeInDaemonThreadAndWait(Runnable, DaemonToken)

Note that DaemonToken is a pretty bad name, so try to think of something better.

PIH needs this implemented in a (backwards-compatible) way that will let us take advantage of this in 1.9.2.