new smb.conf option "panic action"

[Andrew Tridgell]

I suspect that the bug is the lsa lookupsids code that causes smbd to
segv hasn't been picked up until now because other developers don't
look for "INTERNAL ERROR" in their logs and don't use my #ifdef AJT
hack.

To make it easier for everyone to find bugs I have added a new option
"panic action". For example I now have:

  panic action = /usr/bin/X11/xterm -display :0 -e gdb /samba/bin/smbd %d

this tells smbd or nmbd to launch a debugger on the offending process
as soon as it gets a segv. You immediately get a debugger at the right
point in the code.

to support this I have a new util.c function smb_panic() that can be
called whenever weird things happen (like a segv or a parameter out of
range). Please add calls when appropriate.

I hope that if all developers start using "panic action" we will start
to track own these bugs and avoid the problem that smbd appears to
work when in fact it doesn't. 

of course, if you don't run X or use some X auth stuff that prevents
the above working you will need to do something else in "panic action".
Make sure you test it or you might never know that the code is bad!