Contrib r ncdf4

Adding ncdf4 package build with R-3.0.2 (bare and with the R packages). To build ncdf4 I had to build libpng with zlib 1.2.7 because for ncdf4 netCDF is a dependency which is build with zlib 1.2.7

ncdf4 installation with R-2.15.3 uses zlib 1.2.5 and because zlib 1.2.7 is used by many packages (especially netCDF) this leads to many conflicts. To do that I would have to modify the existing libpng configs. So, rather than changing the configs I preferred building a brand new version of libpng and R. 

Also, ncdf is not compatible with R-3.0.2, but ncdf4 actually replaces the former ncdf package, which only worked with netcdf version 3 files.