test_enum.rb: add tests

* test/ruby/test_enum.rb (test_each_slice, test_each_cons): add
  missing tests for Enumerable#each_slice and Enumerable#each_cons.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45602 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
enum.c: fix condition to recycle block argument

* enum.c (dont_recycle_block_arg): fix condition to recycle block
  argument.  lambda with rest can get internal array directly.
  [ruby-core:62060] [Bug #9749]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45603 b2dd03c8-39d4-4d8f-98ff-823fe69b080e