Go to
http://www.linuxpackages.net and search for 'gtkhtml'. There is a pre-built package for Slack 10.1.
That being said, good luck with trying to get Evolution to work. Be prepared to track down a LOT of dependencies, some you can find already compiled into .tgz files, some you'll have to build from source code.
I like Evolution and the fact that it has the Exchange plug-in, but to me, the cost of getting it working under Slack was too great for the perceived benefit.