buildhistory-diff: operate from buildhistory directory
If the cwd is named "buildhistory" and the user hasn't specified an
alternative path on the command line, then assume that the current
directory is the buildhistory directory. This makes it easier to run
buildhistory-diff and also interact with the buildhistory git repository
as you no longer have to jump into the buildhistory directory and up to
the parent again when doing so.
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
