Build recipes don't expand svn keywords

https://code.launchpad.net/~darxus/+recipe/spamassassin-daily

This contains svn keywords: $LastChangedDate$ and $LastChangedRevision$
Because they aren't expanded, the X-Spam-Checker-Version header inserted by builds from it end up broken.

Relevant code lines as retrieved via svn client:

$SUB_VERSION = (split(/\s+/,'$LastChangedDate: 2010-03-30 08:02:18 -0400 (Tue, 30 Mar 2010) $ updated by SVN'))[1];
       ('r' . qw{$LastChangedRevision: 929098 $ updated by SVN}[1]));

Same lines built with this recipe:

$SUB_VERSION = (split(/\s+/,'$LastChangedDate$ updated by SVN'))[1];
       ('r' . qw{$LastChangedRevision$ updated by SVN}[1]));