title: Phabricator arc land won't work because that there are multiple revisions on feature branch
body: <p>I have two branches, started at different points.  They are mostly the same, except for a few extra commits on one of them.  When I try to land that one, I get: </p>
  
  <p>Usage Exception: There are multiple revisions on feature branch 'newbranch' which are not present on 'devel':
  -D newbranch1
  -D othernew branch</p>
  
  <p>Separate these revisions onto different branchs, or use --revision ' to use the commit message from  and land them all.</p>
  
  <p>I can't find any guidance as to how to separate the revisions onto different branches, or what that even means.  Is there any way around this?</p>