title: Availability.h No such file or directory
body: <p>I am trying to build a pre-written app, on OS X 10.5 with the base SDK set to OS X 10.4.
  There are a couple of pre-compiled header files which are returning errors on compile, in CFNetwork.h where it is including Availability.h</p>
  
  <p>"Availability.h - No such file or directory"</p>
  
  <p>I checked the header path and this header is not present in the MacOSX10.4u.sdk /usr/include area.
  It is present in the corresponding 10.5 SDK location.</p>
  
  <p>AvailabilityInternals.h is absent as well. But AvailabilityMacros.h is present. Obviously copying these missing headers over from 10.5 location did not work.
  Am I missing a package in my Leopard install that's causing this? My framework search paths seem to be ok. How to I work around this issue? Please suggest.</p>
  
  <p>Thanks</p>