hdf5_ep

[svn-r18571] Description:
	Bring r18542 from metadata journaling "merging" branch to trunk:

	Bring new object header pin/unpin & protect/unprotect routines and
split-out object header chunk proxy changes from metadata_journaling branch to
"merging" branch, along with some other minor tweaks to clean up compiler
warnings, etc.

	Also: clean up chunk protect/unprotect calls when allocating or freeing
space in a chunk, optimize metadata accumulator code to avoid some re-reading
of information from the file, refactor H5O_pin/H5O_unpin from way they are done
on the merging branch back to way they were previously done on trunk, other
minor code cleanups, etc.

Tested on
        FreeBSD/32 6.3 (duty) in debug mode
        FreeBSD/64 6.3 (liberty) w/C++ & FORTRAN, in debug mode
        Linux/64-amd64 2.6 (amani) w/Intel compilers, w/default API=1.6.x,
                w/C++ & FORTRAN, in production 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 10.6.3 (amazon) in debug mode
        Mac OS X/32 10.6.3 (amazon) w/C++ & FORTRAN, w/threadsafe,
                in production mode