Because executable_path and loader_path are just too inflexible for some
stuff. The rpath is supposed to be set to the Qt Creator app's Contents
folder.
Compiling on 10.4 now requires to enter compatibility mode via
QTC_TIGER_COMPAT env variable or TIGER_COMPAT_MODE qmake variable.

doing it in 1.3 as well to avoid possible later conflicts

Details:  Creator on Linux works now in two modes:
          1) out of the build dir (shadow builds to be tested)
          2) make INSTALL_ROOT=/prefix install