hdf5_ep

[svn-r16847] Description:
	Bring r16846 from revise_chunks branch back to trunk:

	Fix broken (for how long?) H5_ASSIGN_OVERFLOW macro to actually detect
overflows during assignments, along with several errors it [now] detected.

	Cleaned up a fix minor warnings and/or pieces of code also.

Tested on:
	FreeBSD/32 6.3 (duty) in debug mode
	(h5committest not needed - multi-platform test performed on branch)