[MERGE] Fix handling of old merge directives with stricter get_parent_map

[Aaron Bentley]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hi all,

It turns out that revno 3434, which made it illegal to pass None to
get_parent_map, exposed a latent bug in Merger.from_mergeable.  Format 1
merge directives did not provide a base_revision_id, but from_mergeable
assumes one is present (which is always true for Format 2 merge directives).

No bug number for this.  I just ran it down now.

Aaron
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.6 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFINzyE0F+nu1YWqI0RAvNwAJ4pNHdFDkA73A0kWikI38D4nZNUfwCcDUZI
xG6uPw5NXOP/Ij3BNc/aFLQ=
=8oLZ
-----END PGP SIGNATURE-----
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Aaron's mergeable stuff-1935.patch
Type: text/x-diff
Size: 6733 bytes
Desc: not available
Url : https://lists.ubuntu.com/archives/bazaar/attachments/20080523/6b793cdf/attachment.bin