Quincey's fixes for NCF-250, netCDF-4 parallel independent access with
unlimited dimension hanging.  Extending the size of an unlimited
dimension in HDF5 must be a collective operation, so now an error is
returned if trying to extend in independent access mode.

Quincey's bug fixes for parallel build portability, particularly
OpenMPI on MacOS-X.


git-svn-id: https://sub.unidata.ucar.edu/netcdf/trunk@3284 2e3060e4-1ed8-cf1f-9cc2-9586e844a556