Structure growth overrides reinforced block type

[uncorr]

When structures grow, they replace blocks that are clear, such as glass or reeds, with parts of the structure (eg, mushroom or leaves). Citadel does not stop reinforced blocks from being replaced (but still reinforced) by structure parts. Ideally, we'd want to prevent this growth.

Due to the relative simplicity of this task and the non-urgency of this bug, I suggest that we hold solving this one off until we get someone new to spring it on, or use this issue as a friendly starting point for newcomers to the project.

ttk2 informed me that this issue is outstanding, and I couldn't find it in the archives, so I'm creating it now. If we've resolved this, please point me toward that ticket, thanks!