1. First, uninstall Pidgin. I used Synaptic, but you could also do
sudo apt-get remove pidgin
Do not remove libpurple, you'll need that later.
2. Next, install a bunch of dependencies. It turns out it's easiest to install a bunch of pidgin related parts first, then install Carrier later. This gets all the parts you'll need:
sudo apt-get build-dep pidgin
This will install a surprisingly large amount of stuff, mostly because you're installing things to compile from source. You may already have these things, but with a fresh install like I have, I didn't have gcc or the C headers, and so on.
3. Download the source archive for Carrier 2.5.0 from SourceForge:
Of course, if there is a .deb file available, skip step 2 and use the .deb, or if there is a newer source file, use that.
4. Unzip the download, and cd to the top level directory. You can read the INSTALL file, but here are the steps:
This will run for a minute or so, checking that everything installed in step 2 is good.
sudo make install
The "make" step can take a few minutes to run, depending on the speed of your machine. The "make install" step should be pretty quick.
5. Run "carrier" from a command line, or set up a nifty shortcut. The default icon is a duck, so for personal reasons, I was compelled to shout "Duck!" quite loudly.
In this version, and by default, Carrier lets you resize the text area. Annoyance solved!