[crossfire] Minor issues

[Preston Crow]

I've noticed a few minor issues with building the server:

In configure.ac, it is looking python2 instead of python-2.7.  On my 
system it fails to detect with python2, but with a check for python-2.7, 
it works.  I'm not an expert on autoconf, so I don't know if there's an 
easy way to check for either.  (Of course, moving to python 3 would make 
all kinds of sense, but that's another topic.)

In common/init.c, things break badly if someone adds a field in the 
middle of include/global.h.  This can easily be fixed by assigning 
specific field names, though that would move us up to a minimum of C99.

With gcc 10, you get multiple definition errors on shutdown_flag.  This 
should be declared extern in the .h and also declared in one C file.

I'm happy to push commits for the second two issues, but I don't trust 
that my fix for the first one wouldn't break things for other people.  
(I'm not sure if I have permission to push, though.)