add #include <string> to TString.h and provide ifdef for compilers where

string is in global namespace. Also since <string> pulls in <new> we have to
define R__PLACEMENTINLINE for icc otherwise NewDelete.cxx does not compile.

Replace index() by strchr() in TClassEdit.cxx.


git-svn-id: http://root.cern.ch/svn/root/trunk@8089 27541ba8-7e3a-0410-8455-c3a389f83636