Functions determining few direction: the final missing case

By results of Blokhuis, Ball, Brouwer, Storme and Szőnyi, and of Ball, if a function $f:{\mathbb{F}}_q\to {\mathbb{F}}_q$ determines fewer than $(q+3)\mathrm{/}2$ directions, then $f-f(0)$ is linear over a subfield of ${\mathbb{F}}_q$, except possibly when $q$ is even and $f$ determines exactly $q\mathrm{/}2+1$ directions. We settle this case: $f-f(0)$ is then additive. Hence every small minimal blocking set of Rédei type in PG(2,$q$) is linear.