netcdf-c

1. Any test that references nctestserver/NC_findtestserver
   should be under ENABLE_DAP_REMOTE_TESTS.
   Fixed to make sure that this is so.
   Also attempted to fix ncdap_test/CMakeLists.txt,
   but probably got it wrong.
   HT to Nico Schlomer.
2. Attempted to reduce the number of conversion errors
   when -Wconversion is set. Fixed oc2, but
   rest of netcdf remains to be done.
   HT to Nico Schlomer.
3. When doing #2, I discovered an error in ncgen.y
   that has remained hidden. This required some other
   test case fixes.