Before this patch we used to send `double`s over the wire by just
copying them. This is not portable because the internal represenation
of a `double` is implementation specific.
Instead of this, multiply any floating-point numbers that come from
the outside (e.g. JSONs) by 1 million and round them to integers when
handling them.
* Introduce a new param_millionths() that expects a floating-point
number and returns it multipled by 1000000 as an integer.
* Replace param_double() and param_percent() with param_millionths()
* Previously the riskfactor would be allowed to be negative, which must
have been unintentional. This patch changes that to require a
non-negative number.
Changelog-None
89ceb273f5