New git branches created in dialog don't default to tracking when remote is origin

If I'm creating a new git branch, I often want to make tracking the default. We should probably be more liberal in setting the checkbox to selected in various cases:

• if the start point is from remote 'origin'?
• if the remote branch name and local name match?
• according to value from git config branch.autosetupmerge - if true, then any branch with a remote starting point should default to tracking...