hdf5_der

[svn-r16985] Description:
	Interim checkin of work toward closing race condition window which can
cause errors when reading a file that is used for SWMR-write access.

	This change introduces a chunk proxy in the metadata cache, which
participates in the metadata cache's flush dependencies while representing a
raw data chunk in a dataset's chunk cache.

	Also, the extensible array's SWMR behavior is only invoked when the
file is opened for SWMR-write access, allowing more flexibility in flushing
extensible array data structure pieces when SWMR-write is not enabled.

Tested on:
        FreeBSD/32 6.3 (duty) in debug mode
        FreeBSD/64 6.3 (liberty) w/C++ & FORTRAN, in debug mode
        Linux/32 2.6 (jam) w/PGI compilers, w/C++ & FORTRAN, w/threadsafe,
                                in debug mode
        Solaris/32 2.10 (linew) w/deprecated symbols disabled, w/C++ & FORTRAN,
                                w/szip filter, in production mode
        Linux/64-ia64 2.6 (cobalt) w/Intel compilers, w/C++ & FORTRAN,
                                in production mode
        Linux/64-ia64 2.4 (tg-login3) w/parallel, w/FORTRAN, in debug mode
        Linux/64-amd64 2.6 (abe) w/parallel, w/FORTRAN, in production mode
        Mac OS X/32 10.5.6 (amazon) in debug mode
        Mac OS X/32 10.5.6 (amazon) w/C++ & FORTRAN, w/threadsafe,
                                in production mode