As of revision 722891, when I tried to use "--ssl-file /tmp/acl.conf", the broker then used the path "/home/boston/jross/.qpidd//tmp/acl.conf"
I of course meant --*acl*-file in the comment above.
A fix has been commited in Qpid in trunk rev 725303. This issue is tracked in Qpid via QPID-1523
Tested on RHEL4 and RHEL5 on i386, works both with relative and absolute path.