[WIP] Create temporary files w/o race conditions whenever possible (fixes #1145)

[alexvong243f]

This PR could be too ambitious but adding 2 new functions is the cleanest way I can think of to fix #1145 once and for all. These functions cannot be private because they are needed by tests so we append __ to their names.

[cbm755]

I dunno about this...

These functions cannot be private because ...

This bothers me. I guess I'd rather they were private without __ on their names?

[alexvong243f]

I dunno about this...

These functions cannot be private because ...

This bothers me. I guess I'd rather they were private without __ on their names?

Is it possible to call a private function in bist? We don't need the __ trick If there's a way to do so w/o duplicating the code.

[mmuetzel]

Is it possible to call a private function in bist?

That's bug #38776.