When multiple subversion repositories are configured within a single job, the
SVN_REVISION environment variable cannot be used to pass all revision numbers
from the corresponding repositories.
The documentation suggests to use the svnversion command in this particular case
but it is not very practical when the working copy is checked out with the 'svn
update' option enabled: svnversion may report composite revision informations.

I suggest to create a new environment variable, possibly SVN_REVISIONS, to hold
a list of checked out revisions, whose order would match the declaration order
of the repositories in the configuration page.