[DRE-maint] ruby-memoizable is marked for autoremoval from testing

[Debian testing autoremoval watch]

ruby-memoizable 0.4.2-1 is marked for autoremoval from testing on 2014-08-16

It (build-)depends on packages with these RC bugs:
747746: ruby-thread-safe: FTBFS: non_concurrent_cache_backend.rb:10: [BUG] Segmentation fault at 0x000000001b900c