hdf5_ep

[svn-r17786] Description:
	Bring r17749 & 17785 from trunk to 1.8 branch:

17749:
	Refactor v2 B-tree code to bring it further in line with how the fractal
heap code works, to make forthcoming modificaions easier.  Also minor tweaks to
the fractal heap code to clean it up a bit more also.

17785:
	Further refactor v2 B-tree code to bring it closer to modern data
structure designed in the library, mainly by introducing a H5B2_t type so that
the v2 B-tree could be held open, but not require the B-tree header to be
protected the whole time.  A few other minor tweaks as well.

	Also, remove unused 'dirty' flag from fractal heap header.

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 (smirom) 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 10.6.1 (amazon) in debug mode
        Mac OS X/32 10.6.1 (amazon) w/C++ & FORTRAN, w/threadsafe,
                in production mode