Reset release date.
Removed obsolete debugger files.
Fixed DebugAction registering for :before events.
Deleted most references to compare_by_identity.

Hash#compare_by_identity was not introduced in 1.8.7. Remaining references
are in:

* spec/ruby/core/hash/assoc_spec.rb
* kernel/common/marshal.rb
Merge branch '1.8.7' of git://github.com/rubinius/rubinius into 1.8.7_hash_hamt