start splitting up the cache tests
Test that discarding a thin doesn't free shared blocks.

Failing scenario from jminter
remove some debug
add tests/cache/cache_stack.rb
add policy.rb
add deploy target to Rakefile
Try and get FakeDiscard tests working again
Fix bug in with_custom_data_pool
fix some discard tests
Merge remote branch 'ejt/master' into devel
clarify intent of the no passdown FakeDiscard tests