fix for btdownloadgui tornado alternative

[Toby Kelsey]

If like me you've updated bittornado-gui from breezy-updates you might
find that the tornado version has disppeared from the alternatives for
btdownloadgui.  Here are the commands to add it back as an alternative
and set it as the default.  It took me a while to figure out the exact
syntax (the manpage confuses names and absolute paths).

Set up the alternative (ignore any line-breaks due to the mailreader):
$ sudo update-alternatives --install /usr/bin/btdownloadgui
btdownloadgui /usr/bin/btdownloadgui.bittornado 120 --slave
/usr/share/man/man1/btdownloadgui.1.gz btdownloadgui.1.gz
/usr/share/man/man1/btdownloadgui.bittornado.1.gz

Chose the tornado version:
$ sudo update-alternatives --auto btdownloadgui

or you can select it manually with:
  $ sudo update-alternatives --config btdownloadgui

Some final checks:
$ update-alternatives --display btdownloadgui
$ ls -l /usr/bin/btdownloadgui

Using update-alternatives is more clunky and brittle, but fixing the
symlinks directly could create database inconsistencies (an example of
'user-friendly' software making things worse).

Hope this helps,
Toby