* string.c (rb_fstring): fstrings should be ELTS_SHARED.
  If we resurrect dying objects (non-marked, but not swept yet),
  pointing shared string can be collected.
  To avoid such issue, fstrings (recorded to fstring_table)
  should not be ELTS_SHARED (should not have a shared string).



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43887 b2dd03c8-39d4-4d8f-98ff-823fe69b080e