netcdf-c

Support user-specified hdf5 and hdf5_hl libraries

If the netcdf cmake build is configured with explicitly specified hdf5 c and hl libraries:
```
    -DHDF5_C_LIBRARY:PATH=${ACCESS}/lib/libhdf5.dylib \
    -DHDF5_HL_LIBRARY:PATH=${ACCESS}/lib/libhdf5_hl.dylib \
    -DHDF5_INCLUDE_DIR:PATH=${ACCESS}/include \
```
Then it looks like the HDF5_C_LIBRARIES and HDF5_HL_LIBRARIES variables do not get set and then this causes the HDF5 libraries to be omitted from the `TLL_LIBS` symbol in liblib/CMakeLists.txt.  This is subsequently used to build `ALL_TLL_LIBS` which is used for `LIBS` which is output as the `Extra libraries:        @LIBS@` in libnetcdf.settings.in 

The output for `-- Linking against:` is also incorrect as it omits the hdf5 libraries:   Output without suggested change:
```
-- Linking against:      /usr/lib/libdl.dylib;/usr/lib/libm.dylib;/opt/local/lib/libz.dylib;/opt/local/lib/libcurl.dylib
(later in file)
Extra libraries:	-ldl -lm -lz -lcurl
```
versus output with suggested change:
```
-- Linking against:      /Users/gdsjaar/src/seacas-parallel/lib/libhdf5_hl.dylib;/Users/gdsjaar/src/seacas-parallel/lib/libhdf5.dylib;/usr/lib/libdl.dylib;/usr/lib/libm.dylib;/opt/local/lib/libz.dylib;/opt/local/lib/libcurl.dylib
(later in file)
Extra libraries:	-lhdf5_hl -lhdf5 -ldl -lm -lz -lcurl
```
This also causes a link failure when building libnetcdf.dylib