Log Message:
Update to 1.6.21.  Notable changes:

  - Added CIDR support to eggdrop. This includes accepting and matching b/e/I
    masks and user hosts in cidr notation.
  - Added a msg-rate config variable, to replace the current #define msgrate
    in server.mod.
  - Replaced most dns.mod preprocessor definitions with config variables.
  - Added a configure option to set the handlen while keeping compatibility with
    the older method of editing eggdrop.h directly.

  - Explicitly offer both --enable-tcl-threads and --disable-tcl-threads
    configure options that can forcefully enable or disable threaded Tcl
    library support.

  - Fixed a remote DoS in the CTCP parsing code introduced by the servmsg.c
    buffer overflow patch by Nico Golde.
    Reference: CVE-2009-1789
  - Work around Tcl8.5.10 bug 3371644 (strings starting with # could crash
    in Tcl_ConvertElement()).
  - tcl_maskhost could crash the bot.
  - Fixed a potential crash in read_lang() with lines > 512 characters in
    language files. Added support for lines of unlimited size.
  - Fixed dns.mod SIGBUS crashes on 64-bit Sparc.
  - Fixed a crash when restarting, related to bind log.