Fixed getPercentileAtValue() to return the highestEquivalentValue() of the value at the requested percentile.
Before this change, the returned value for a given percentile could be lower than the actual value recorded (as low
as the lowestEquivalentValue()). Given that a value at a percentile X means "the value which X% of recorded data is
less than or equal to", the highest possible equivalent value should be returned.

This (presumably) fixes https://github.com/HdrHistogram/HdrHistogram/issues/9 , since percentile output was
already using the highestEquivalentValue().
Merge remote-tracking branch 'origin/master'