fix force_disconnect test on perl < 5.9.0

This fixes the following test failure on perl 5.8.8:
t/30-disconnect.t .. 1/? Not an ARRAY reference at /root/.cpan/build/MogileFS-Client-1.17/blib/lib/MogileFS/Client.pm line 199.
# Tests were run but no plan was declared and done_testing() was not seen.
t/30-disconnect.t .. Dubious, test returned 255 (wstat 65280, 0xff00)

MogileFS::Client utilizes the fields pragma for defining objects. Before perl 5.9.0 fields utilized psuedo-hashes for the objects, which are not completely compatible with regular blessed hashes.