**System Information**
Operating system and graphics card
Win7 32 bit
Nvidia G-Force 660 GTX
**Blender Version**
Broken: 2.69.0 r60991
**Short description of error**
In the python API, when you want to access an object's material slot (object.material_slots),
you can use its name (string key in material_slots collection), which is nice.
But on the other hand, two material slots can have the exact same key-name, which means that you can only access one of them via its key while the others won't be accessible.
Material slots should probably have name auto-incrementing like materials, object names, etc.
**Exact steps for others to reproduce the error**
Based on a (as simple as possible) attached .blend file with minimum amount of steps
1. Open new file.
2. Select default cube.
3. Add two materials slots through material tab on properties window.
4. Assign the same material to both slots.
3. Open python console:
>>> len(C.object.material_slots)
2
>>> C.object.material_slots.keys()
['Material', 'Material']