Debian package name ends in a 'd'.

[Package on Ubuntu Packages](http://packages.ubuntu.com/trusty/libmemcached-dev).

After having issues where pylibmc couldn't access memcached on Ubuntu 14.04LTS, eventually tracked it down to libmemcached-dev not being installed. Looked into the code and saw that it was attempting to install libmemcache-dev rather than libmemcached-dev.