Add 3 pixels to the guide star selection edge padding

[jeanconn]

Add 3 pixels to the guide star selection edge padding

[jeanconn]

The different question is if we want to include the stars in the 3pix region in the candidates table (so they will go through the other checks). I don't know if it would be helpful to have debug information on them if we get desperate when looking for stars and trying to add one manually.

If we want to go that way, it seems like we'd leave the out-of-bounds check limits the way they were and then exclude the stars near the edge with a new check + logging of rejection reason etc.

[taldcroft]

For now keep it simple. I almost even regret making the comment that resulted in the last commit. This patch needs to be pretty tight. And it should be against 4.3.x as a bug fix. We can do something similar against master but are a little less constrained.

[taldcroft]

... if we want to include the stars in the 3pix region in the candidates table

With a broader perspective now, I think the answer is a firm no. If there is a problem then the intent is for roll optimization to pick them up.

[taldcroft]

@jeanconn - looks good to merge to me. If you have no further reservations then let's get this into master.

[jeanconn]

I just double-checked that this actually passes tests (it had been a while) and I think this is good.