Have dispatch() track the procedure name, use in errors

[inexorabletash]

• [ ] wrap dispatch() method body in a try/finally
• [ ] push/pop the target name on a stack
• [ ] add internal currentProc() method
• [ ] add hook to error message formatting to get current proc name
• [ ] use in all errors rather than hardcoding method name

[inexorabletash]

Tricker due to async execution - need to use promiseFinally