error in threshold math when adding intersection points ( for 1 point below/upper the threshold)

[jerikojerk]

please replace:
near jquery.flot.threshold.js:65

var interx = (x - origpoints[i - ps]) / (y - origpoints[i - ps + 1]) * (below - y) + x;

with

var interx = x+( below- y )*(y-origpoints[i - ps + 1])/( x- origpoints[i - ps] );

i think it does better results when graphing lines.

[dnschnur]

Fixed in master; thanks for the note!