hdf5_der

Committed fix to the infinite recursion bug that Vailin encountered
when testing page buffering with test/fheap.c.  Also, modifications
to test/cache.c to reflect changes in cache behaviour caused by
H5C_make_space_in_cache() returning success without any other
activity on re-entrant calls.

In passing, also un-commented SWMR / cache image test in test/cache_image.c,
and added code to skip it.  This should be removed when the necessary
support make it in from trunk.

Tested serial, serial/check-vfd, serial/production, parallel,
       parallel/production on jelly