Fix documentation for running git commands

Fixes #204

Fix git version parsing when there are spaces

Fix write_gitignore for git version >= 2.7

As of git version 2.7 it is no longer necessary to include parent
directories in the list of files not to be ignored.

This fixes #195.

Thanks to Matt S Trout

This reverts commit d5c11e43.

Turns out you need to `apt-get update` all of a sudden...

This reverts commit 3e6f3366.

Seems their infrastructure migration went not quite as expected...

Fix tests under git-2.2

We will fetch more data than needed with Git 1.8, but other than that...

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.