Merge branch 'tk/simple-autosetupmerge'

Merge branch 'tk/simple-autosetupmerge'

"git -c branch.autosetupmerge=simple branch $A $B" will set the $B
as $A's upstream only when $A and $B shares the same name, and "git
-c push.default=simple" on branch $A would push to update the
branch $A at the remote $B came from.  Also more places use the
sole remote, if exists, before defaulting to 'origin'.

* tk/simple-autosetupmerge:
  push: new config option "push.autoSetupRemote" supports "simple" push
  push: default to single remote even when not named origin
  branch: new autosetupmerge option 'simple' for matching branches