This sadly means that buildings cannot be placed where destroyed func_breakables and func_weldables are. Unfortunately, the fix also meant structures could be placed inside railings which would immediately cause them to sink
This is a fix for Issue #55. Changes made:
* Server ignores intangible entities when determining if a building placement is valid (fixes func_breakable issue)
* If a func_weldable has the "welds open" spawnflag set, then upon completing the weld when it plays the break effect, it will become fully intangible. It will reset upon round restart.
Fix by @RGreenlees
