hdf5_ep

[svn-r17460] Description:
	Bring r17459 from trunk to v1.8 branch:

	Correct bad interaction between non-zero userblocks with non-zero
alignments.

	Also add some additional range checking and tests for invalid userblock
sizes.

Tested on:
   FreeBSD/32 6.3 (duty) in debug mode
   (h5committested on trunk)