Make svnserve require --inetd to use stdin/stdout

A patch to do this is attached.  This issue is created to hold the patch and to
provide a reference for voting in the 1.0-stabilization STATUS file.  The
mailing list discussion is here:

http://www.contactor.se/~dast/svn/archive-2004-01/0051.shtml

--------------------------- log message -------------------------------
Make svnserve show an error message and usage if it is run without any
arguments. Add a new -i/--inet option to make svnserve use
stdin/stdout (which was the old default). Add a new -F/--foreground
option to prevent svnserve from daemonizing (which is useful for
debugging).

* subversion/svnserve/main.c

   (run_mode): New enum.

   (svnserve__options): Add -i/--inetd and -F/--foreground.

   (main): Use run_mode instead of several booleans. Show error message
   and usage if no mode is selected. Handle the new inetd and
   foreground options.

* subversion/svnserve/svnserve.8

   Updated to match the changes to subversion/svnserve/main.c.

Original issue reported by bliss