compile.c: add opt_aset instruction for faster Hash#[]= and Array#[]=

* compile.c (iseq_specialized_instruction): emit opt_aset instruction
  to optimize Hash#[]= and Array#[]= when called with Fixnum argument.
  [Bug #9227] [ruby-core:58956]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44136 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
hash.c: reject should return a plain hash

* hash.c (rb_hash_reject): return a plain hash, without copying
  the class, default value, instance variables, and taintedness.
  they had been copied just by accident.
  [ruby-core:59045] [Bug #9223]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44137 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
Merge commit '740535f843d65be45732e45b9fc07eadc4d63ba7' into 2.1