coordinate variables and their associated dimensions occurs in any
subgroup, rather than just the root group. If this occurs, the
variable attribute "_Netcdf4Dimid" is created for every dimension
scale.
Also add a test for this bug fix in tst_dims3.nc, based on Pedro
Vicente's demo.
enhancements, based on contributed code from Martin van Driel, to
support -v, -g, -V, and -G options for selecting groups and variables
in output. Fix all clang warnings from nccopy and ncdump sources, as
well as a few other cleanup changes to testing code.
