hdf5_ep

[svn-r8953] 
Purpose:
Bug fix

Description:
When a simple dataspace is created, its extent should be set before using it,
or it will silently function as a NULL dataspace.

Solution:
Added checks on user-supplied dataspaces.  Now dataspaces without extents set
will throw errors; users must explicitly set a dataspace to be NULL.

Platforms tested:
sleipnir, windows