ENH: Add option to bootstrap script to enable Qt dialog.

  - Add --qt-gui and --no-qt-gui options
  - Add --qt-qmake=<qmake> option to help locate Qt
  - Build more commands during bootstrap to help FindQt4.cmake:
    MATH, GET_DIRECTORY_PROPERTY, EXECUTE_PROCESS,
    SEPARATE_ARGUMENTS
  - Bootstrapping with the cmake-gui is now possible in MSys