hdf5_ep

[svn-r13440] Description:
	Revise latest form of superblock format pretty drastically, to
eliminate unused fields and move rarely used fields into superblock extension.

	Finished removing last vestiges of references to (never used) i"shared"
object header message ID.

	Added object header messages for non-default v1 B-tree 'K' values
and for driver info.

	Updated testfiles to reflect size changes, etc.

	Various minor cleanups, etc.

Tested on:
	FreeBSD/32 6.2 (duty)
	Mac OS X/32 10.4.8 (amazon)