Handle unloaded units being referenced outside factory

[ibboard]

Now that we're handling requirements then the Race factory is handing work off to other factories. These other factories have to make certain assumptions about how they can work (e.g. they have to assume that they could be working with any factory). These assumptions cause problems when it comes to requirements referencing units that haven't been loaded yet - Race.GetUnitType(id) fails because the load has been triggered but the unit isn't loaded yet, so it returns a null.

We can't just wait for loading to complete before Race.GetUnitType(id) completes, because that would hang the factory. Instead, we need to standardise things so that external factories can use the Race factory to get at objects.

[ibboard]

In [951]:

Re #353: Handle unloaded units being referenced outside factory

• Remove inheritance prior to creation of more generalised sub-factory inheritance
• Create helper class that contains the only common code from old inheritance to keep duplication down

[ibboard]

In [952]:

Re #353: Handle unloaded units being referenced outside factory

• Create interface for race factories
• Start to pull out common methods and add "try unit and fall back to factory" method for getting unit types
• Make XML Race Factory implement interface
• Use new factory

[ibboard]

In [953]:

Re #353: Handle unloaded units being referenced outside factory

• Add mock factory and use it in tests

All tests now pass (including tests that started failing because of unit loading order - triggered by requirement changes)

[ibboard]

In [954]:

Re #353: Handle unloaded units being referenced outside factory

• Remove old named method and update references

[ibboard]

In [955]:

Fixes #353: Handle unloaded units being referenced outside factory

• Update final reference