numeric.c: optimize for Bignum

* numeric.c (rb_int_succ, rb_int_pred): shortcut optimization for
  Bignum.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39593 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
enumerator.c: allow Bignum for with_index

* enumerator.c (enumerator_with_index_i): allow Bignum as offset, to
  get rid of conversion exception and integer overflow.
  [ruby-dev:47131] [Bug #8010]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39594 b2dd03c8-39d4-4d8f-98ff-823fe69b080e