rlm_pap code tidy

[Alan DeKok]

Matthew Newton wrote:
> 52b68318 -
>   moves header-like stuff into rlm_pap.h

  That's my only concern.  Moving C structs into header files is bad form.

> It now uses a function pointers to select the right auth function
> depending on the config attribute found. I was slightly worried
> that calling functions on this might slow things down a bit.
> However, running 1000 auths in a tight loop (non-threaded server,
> debug off) shows essentially no difference on my system - over
> three runs, old code avg 23.516s, new code avg 23.464s.

  Yeah.  It's better that way.  The old code was... interesting.

  Alan DeKok.