add tests for float conversions to u64

add tests for float conversions to u64

Note:
I removed the test that used sin()
function because it makes no sense
to use that there and besides I could
not get the test to work because
sin requires -lm linked but for some reason
make does not compile with -lm and
I get errors like undefined symbol sin.
Coerce function should do the same thing
for the purposes of that test.