using numeric input
When using numeric input to move strips, the strip extent clamping code could
end up prematurely truncating one endpoint. This was because the clamping code
uses the values of the other end (e.g. end for start, and start for end) as one
of the limits on its allowable range to prevent inverted strips.
Now we just set these values twice - the first time, one of the endpoints may
still get truncated (while the other one will be able to go to its correct
value), then the second time both will get set correctly (and validated too).
bfa065f10c