When using the hudson maven release plugin, maven will trigger a SCM tag.

This command will be ran on the user's login shell and won't reuse the svn
permissions stored by hudson.

The hudson user created by the current debian package doesn't allow shell, so
the command will not be able to reuse any locally configured subversion
logins.

The patch works around the issue by assigning a shell to the hudson user
created by maven. The patch doesn't address existing hudson users.

I am not sure if this change needs to be committed or if because of security
issues, we should let users manually modify the system configuration.