Re: [PATCH 2/2] rebase -i: be careful to wrap up fixup/squash chains

Let me see if the code is easily grokkable by (trying to) follow aloud.

    We used to refrain from going into this big else clause that
    does the fixup-squash handling when is_clean is false,
    current-count is not yet zero, head and to-amend are different
    commits or stopped-sha file is missing.  The updated code still
    refrains from going into the big else clause under exactly the
    same condition, but it learned to clean up the state, when the
    _next_ one is not a fix-up, i.e. when we are looking at the last
    fixup/squash in the current chain.  And the lack of clean-up
    would have resulted in the next step misbehaving.

I see a few calls to is_fixup(peek_command()) and a local boolean variable final_fixup used in this function. I have to wonder if it makes the resulting code, especially the above part, easier to follow and understand, if the function peeked todo-list to check if we are dealing with the final fix-up in a chain very early just once, and used it to see "are we doing the final fixup/squash in the current chain?" throughout the rest of the function.

	Side note: I actually think that the existing final_fixup
	boolean means something different (iow, final_fixup is not
	set inside the new "clean-up" code above, even though we
	dealt with the last one in the fix-up chain, and that is not
	a bug---which means that "final_fixup" does not mean "we are
	dealing with the last one in the fix-up chain"), which may
	want to be clarified a bit with in-code comment near where
	the variable is defined for the function to be readable.

In any case, thanks for fixing this, which seems to have appeared in Git 2.18. Let's fork a topic from maint, cook it in 'next' and aim for eventually merging it down for both 2.19 and 2.18 tracks.