string.c: pool only bare strings in fstring
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51360 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
string.c: pool only bare strings in fstring
fstring if it has extra attributes, not the fstring itself.
[ruby-dev:49188] [Bug #11386]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51360 b2dd03c8-39d4-4d8f-98ff-823fe69b080e