OMERO5.1DEV__15: fix tolerance types with nonegative_float

The units PR incorrectly rolled back the cutin/cutout
types to int. Further, there wasn't a definition for a
nonnegative_float. Both of these have been adjusted now.

/cc @jburel
--no-rebase
Interesting! Thank you. This is likely the cause of much of merge-integration's unhappines. /cc @sbesson