poincareCircuitBreaker requires the Back key to be pressed for at least
50 ms before interrupting a computation.
This is effectively invisible for the user, but fixes a bug in
Calculation :
- When leaving the additional results for a result using units by
pressing the Back key, a reduction preceding a call to removeUnits
would be interrupted, causing an undefined behaviour.
Change-Id: Iec667ae964f190de2171850cc22e1726959e6cb5