A comment from Carlos has given an additional pointer that I wanted to highlight. It appears when he ran through the methodology an openssl library wasn’t installed so the compile of aircrack-ng failed. He was so kind as to also leave the apt-get command to get this fixed. In the future go ahead and install the openssl library at the time that you also install subversion. If you’ve already got the lib, apt-get won’t really care so no harm, no foul.
pi@raspberrypi ~ $ sudo apt-get install subversion libssl-dev pi@raspberrypi ~ $ svn co http://trac.aircrack-ng.org/svn/trunk aircrack-ng Checked out external at revision 2177. Checked out revision 2177. pi@raspberrypi ~ $ cd aircrack-ng
The rest can be found in the previous post here