vchoi_fork

[svn-r365] Problems:
When data is read or written out, some layers did an immediate
return(SUCCEED) if number of elements to be accessed is zero.
This caused problems when collective access is used.  In a
collective call, all processes in a communicator must call
the lowest layer of MPIO routines even if some of them happen
to access no date.

Solutions:
Eliminated all those pre-mature return if #element==0;