Removing some methods that appear not to be used

It looks like perhaps these were put in place before git solo was fully
supported.  There is probably some more cleanup that needs to happen to
this effect.
Adding fix for bug with no author set

Error was that git-duet will print error messages but allow the commit
to succeed, returning zero.  This fix raises another error so that the
commit fails (and returns a 17).  Also added corresponding specs.