I'm trying to get chemruby running under both OSX 10.3.9 and CentOS5.  Both installing from the gem or the tarball seem
to work at first, but require or the rake test fail complaining about missing 'dbm'.

here's the detailed error message:
[root@localhost chemruby-1.0.0]# rake test
(in /tmp/chemruby-1.0.0)
cd ext/
make
make: Nothing to be done for `all'.
cd -
./lib/chem/utils/graph_db.rb:3:in `require': no such file to load -- dbm (LoadError)
        from ./lib/chem/utils/graph_db.rb:3
        from ./lib/chem/utils.rb:11:in `require'
        from ./lib/chem/utils.rb:11
        from ./lib/chem.rb:25:in `require'
        from ./lib/chem.rb:25
        from ./test/all.rb:4:in `require'
        from ./test/all.rb:4
        from ./test/test_subcomp.rb:4:in `require'
        from ./test/test_subcomp.rb:4
        from /usr/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake/rake_test_loader.rb:5:in `load'
        from /usr/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake/rake_test_loader.rb:5
        from /usr/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake/rake_test_loader.rb:5:in `each'
        from /usr/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake/rake_test_loader.rb:5
rake aborted!
Command failed with status (1): [/usr/bin/ruby -Ilib:ext:lib "/usr/lib/ruby...]

(See full trace by running task with --trace)