Change processing of atoms in ruby_add_rdepend and ruby_add_bdepend to

Change processing of atoms in ruby_add_rdepend and ruby_add_bdepend to
make it possible to process complex dependency strings, such as

|| ( virtual/ruby-test-unit dev-ruby/test-unit:2 )

which is going to be common for test-unit-2 compatible packages; to
have a proper dependency tree.

This, theorically, can also drop the need for the 2-ary calls for
ruby_add_bdepend and ruby_add_rdepend.