Item name constraint violations should also disable any Save buttons

[Viqsi]

VV got slightly misled when she attempted to save a custom variable named "BP" (the minimum is 3 characters). Apparently the warning message below the field went unnoticed, and the "Save" button was turned on anyways, and when the "nope, not allowed" error message came up the explanation didn't get noticed. So having such constraints prevent saving from being possible might be a Good Idea.

(The bigger problem - that folks are now giving feedback of "it didn't work" without actually looking at the explanations the error messages offer - would be a separate issue. Harrumph.)