Issue 26: cvs_import might create multiple heads after multiple imports

Reported by Unknown User, Jul 7, 2005

(This entry was imported from the savannah tracker, original 
location: https://savannah.nongnu.org/bugs/index.php?13662)

after importing a newer cvs history on top of an older one (already 
in monotone) there is a possibility for the ancestry to be created 
differently in the second import, leading to multiple heads

monotone version:
-----------------
monotone 0.20 (base revision: 
44ed8807bead656889fb5022f974e13a7169098c)
Running on: Darwin 8.1.0 Darwin Kernel Version 8.1.0: Tue May 24 
16:21:14 PDT 2005; root:xnu-792.1.5.obj~8/RELEASE_PPC Power Macintosh
Changes since base revision:

new_manifest [5ce921ee9229c7e7f2f07d77c67de1feee633351]

old_revision [44ed8807bead656889fb5022f974e13a7169098c]
old_manifest [5ce921ee9229c7e7f2f07d77c67de1feee633351]