hdf5

[svn-r19396] Description:
	Bring back various modifications to the v2 B-trees that were introduced
in the revise_chunks branch but aren't dependent on any file format or API
changes.

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/default API=1.8.x,
                w/C++ & FORTRAN, w/threadsafe, 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, w/threadsafe, in production mode
        Linux/PPC 2.6 (heiwa) w/C++ & FORTRAN, w/threadsafe, in debug mode
        Linux/64-ia64 2.6 (cobalt) w/Intel compilers, w/C++ & FORTRAN,
                in production mode
        Linux/64-amd64 2.6 (abe) w/parallel, w/FORTRAN, in debug mode
        Mac OS X/32 10.6.4 (amazon) in debug mode
        Mac OS X/32 10.6.4 (amazon) w/C++ & FORTRAN, w/threadsafe,
                in production mode
        Mac OS X/32 10.6.4 (amazon) w/parallel, in debug mode