Fixes #8 by rebasing all merge-base commits. Not sure if it also works for very complex situations like

a-b-c-d-e-f
  \
   g-h-i
      \
       j-k

or

a-b-c-d-e-f
  \    /
   g-h-i

But it does work for testytest.sh, which creates

     g
    /
a-b-c-d
  \
   e-f

and becomes

     g
    /
0-1-2-3
  \
   e-f

Then running git-linearize from any other branch will just work!
Also not sure what happens if there
Sorry for not writing it all in the tests, I tried, but didn't really know how to use the bats files...