useradd segfaults if too many users in one group

This is a redhat hat bugzilla 
https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=125510
but the problem is not RedHat specific.  The problem is there is no 
bounds checking in gshadow.c:list() and the static buffer is being 
overfilled, trashing whatever is next in memory.

I have a patch which does dynamic allocation similar to sgetgrent.  If 
this is the right place, I would like someone to check it.

John.

-- 
John Newbigin
Computer Systems Officer
Faculty of Information and Communication Technologies
Swinburne University of Technology
Melbourne, Australia
http://www.it.swin.edu.au/staff/jnewbigin