This fixes Object.getOwnPropertyDescriptor to report string character
elements as enumerable in accordance with the spec.

BUG=v8:862
TEST=mjsunit/get-own-property-descriptor

Review URL: https://chromiumcodereview.appspot.com/9447053
Patch from Ioseb Dzmanashvili <ioseb.dzmanashvili@gmail.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10822 ce2b1a6d-e550-0410-aec6-3dcde31c8c00