merge revision(s) 39722,43929: [Backport #9178]

	* enumerator.c (enumerator_with_index): try to convert given offset to
	  integer. fix bug introduced in r39594.

	* enumerator.c (enumerator_with_index): should not store local variable
	  address to memoise the arguments.  it is invalidated after the return.
	  [ruby-core:58692] [Bug #9178]


git-svn-id: svn+ssh://svn.ruby-lang.org/ruby/branches/ruby_1_9_3@44745 b2dd03c8-39d4-4d8f-98ff-823fe69b080e