[Patch] Port from v7 stl_function clean-up

[Paolo Carlini]

Benjamin Kosnik wrote:

>Can you hold off on all porting from v7 until the versioning patch goes
>into mainline? I expect this within the next 24 hrs.
>
>Thanks for your cooperation.
>  
>
No problem. In fact, this specific patch touches only stl_function.h and
adds a testcase, i.e., should not interfere at all with anything else,
but can definitely wait until tomorrow!

Paolo.