lcl: gtk2: fixed ShowHide for TCustomTabControl

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@45395 4005530d-fff6-0310-9dd1-cebe43e6787f
IDE: enabled new external tools by default, use old code with -dEnableOldExtTools

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@45396 4005530d-fff6-0310-9dd1-cebe43e6787f