Subject says it all, more in the patch log message at:
http://people.apache.org/~rjung/patches/apr-trunk-fix-broken-installation-of-apu_h.patchOn the long term apu.h might go completely, but until now it is still referenced in a lot of installed header files. So e.g. httpd trunk doesn't compile against an installed apr 2 because apr_hooks.h includes apu.h.
Rainer
