bundle: exclude csets given in --base, unless they are in --rev (issue1910)
Thanks Jesse Glick for the first version of this patch.
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<td class="description"><a href="/rev/1b0e7ece6bd6"><a href="http://bts.example.org/issue123">Issue123</a>: fixed the <i class="x">bug</i>!</a><span class="branchhead">default</span> <span class="tag">tip</span> </td>
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