Straight picked UV Samples and automatically detects
if it needs to be straighten to U or V axis.
Select With the Pick Cursor
Add Selection With SHIFT
Right Click to Finish
Ctrl + Z to Undo Everything
It is a script.
Drag & Drop it to your ToolBar or MainShelf, or execute it from your Script Editor.
I had a request to change the Undo.
Instead of undo everything, undo step by step.
Version updated. Same Link.