measure control - wrong measure when moving fast

[elemoine]

the issue can be observed on < http://www.openlayers.org/dev/examples/measure.html>:

• select measure distance
• draw a point
• move the mouse a bit to create a small distance
• draw another point and move the mouse very quickly far away from the first point
• observe the measure result
• draw a third point very close to the second point
• observe the measure result, it will be smaller than the previous one

[elemoine]

tests pass in FF3 and Chromium6.

[fredj]

looks good

[elemoine]

(In [10407]) measure control - wrong measure when moving fast, r=fredj (closes #2691)