patch ping (was: libguile/print.c fixes)

[Paul Jarc]

Any feedback one these two patches?  One is a bugfix; the other is a
straightforward new POSIX function.  My paperwork is done, and I can
repost the patches if needed.

I wrote:
> In case someone else is less busy... top-level ChangeLog:
>       * configure.in: check for setgroups.
> libguile/ChangeLog:
>       * posix.c (scm_setgroups): new function.
>       * print.c (scm_print_symbol_name): add comments and fix bugs
>       for #{1}#, #{'x}#, and #{}\#\ }#.


paul