correction from last commit
CMake: quiet warnigns with 3.0
Regression Bugfix T40332: Bad driver behaviour on small distances.

!!! ANIMATORS/RIGGERS PLEASE TEST !!!

I've reduced the size of the threshold for the keyframe lookup here. This threshold
determines the minimum time in frames between keyframes (i.e. "how close" to each
other they can get). Making this too small causes problems like T39207, but it seems
that the threshold we've been using makes it impossible to get accurate behaviour on
driver curves with keyframes, when the driver target only moves 2cm (i.e. 0.02 BU).

So far, all of the test cases from T39207 seem to work fine, as well as Caminandes 2
files, and Kenny the Caterpillar. The Kiribati rigs/shots (thanks jpbouza for helping
to check on these!) also seem to be fine.