Add security note on CoreDumpDirectory for Linux.

    operating system is not configured to write core files to the working directory

    of the crashing processes.</p>

    <note type="warning">

      <title>Security note for Linux systems</title>

      <p>Using this directive on Linux may allow other processes on

      the system (if running with similar privileges, such as CGI

      scripts) to attach to httpd children via the <code>ptrace</code>

      system call.  This may make weaken the protection from certain

      security attacks.  It is not recommended to use this directive

      on production systems.</p>

    </note>

    <note><title>Core Dumps on Linux</title>

      <p>If Apache httpd starts as root and switches to another user, the

      Linux kernel <em>disables</em> core dumps even if the directory is