building Windows, install DirectX headers package before building SDL,
so that the SDL DLLs include the DirectX backends.
Subversion-branch: /buildscripts
Subversion-revision: 2472
INSTALL_DIR (which may not have a share/aclocal).
Set PATH to include $INSTALL_DIR/bin, so that SDL is correctly detected
if it has already been built and installed.
Exit if an error occurs during the autogen stage.
Subversion-branch: /buildscripts
Subversion-revision: 1945
