Fix sentries being deployable through doors and thin walls

[GoogleCodeExporter]

Further description of the defect:
This bug has been around for way too long and really destroys any sort of 
challenge on the beginning of the deima surface bridge.

I will add a cvar to enable/disable this fix.

Original issue reported on code.google.com by ibe...@gmail.com on 15 Nov 2012 at 10:01