Fix tests under git-2.2

vcsh: Always fast forward initial merge

Fix broken list-tracked-by -- list_tracked expects repository at $2

github: Closes richih/vcsh#168

github: Closes richih/vcsh#181

Ignore `merge.ff = no` if set in .gitconfig.

t/300-add.t ........ "my" variable $output masks earlier declaration in
same scope at t/300-add.t line 32.

`--nocheck-order` is only supported by GNU `comm`, but it isn't
necessary anyway because we sort the inputs first.

No help, completion, or other related updates

'branches' directory was obsolete and finally removed in recent git
versions.

only shows repositories with changes, which makes it suitable to be run
during login shell startup.

Needs more cowbell