codetools: TStringTree: thread safe

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@42221 4005530d-fff6-0310-9dd1-cebe43e6787f
LCL: dialogs: allow defining own messagedlg overloads

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@42222 4005530d-fff6-0310-9dd1-cebe43e6787f