vchoi_fork

[svn-r20496] Bug 1386 - allow dimension size to be zero even though it isn't unlimited.  I made a change in H5Sset_extent_simple to
forbid setting the dimension size bigger than existing maximal size.  In this checkin, I restored it to the previous 
behavior that any change will wipe out previous record of dimensionality.

Tested on jam - a simple change.