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

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


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@44150 b2dd03c8-39d4-4d8f-98ff-823fe69b080e