[patch]: Remove unnecessary overloads in stl_function.h

[Paolo Carlini]

caj wrote:

> In stl_function.h, the various mem_fun templates are defined. I was 
> digging through this when I noticed that there was a set of 
> specialised overloads for void. These are noted as only been necessary 
> if the compiler doesn't support partial specialization, and of course 
> g++ does!
>
> The following patch removes the unnessasary overloads and adds a test 
> file.

Nobody commented, to date, therefore I'm going to install in the v7 
branch this nice clean-up. Only, I'm curious about the history of this 
HP/SGI workaround: Matt?!?

Otherwise, after proper testing, I will go ahead...

Paolo.