1. The duplicate name checking in oc2 was
   effectively o(n cubed); modified to be
   o(n squared).
2. If the list of prefetched variables is too long,
   (something on the order of 400 variables), then
   the server may reject it. Modified code so that
   in the case that the set of prefetch'd vars is
   the in fact all variables, it does not create a long
   request. This does not actually solve the problem
   if the prefetch list is long, but not all inclusive.


git-svn-id: https://sub.unidata.ucar.edu/netcdf/trunk@3358 2e3060e4-1ed8-cf1f-9cc2-9586e844a556