* eval.c (rb_eval): needs to guard intermediate string objects.
	  based on a patch from Brent Roman <brent AT mbari.org> a
	  [ruby-core:22584].


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8_7@23626 b2dd03c8-39d4-4d8f-98ff-823fe69b080e