Changed how HAVE_PREP is set in R/prep.R. It defaults to FALSE, which is
appropriate on windows systems.  If prep is available on unix-likes,
issue a sed command in configure.ac to change it to TRUE.
Create an empty configure.win, which avoids a warning on windows builds,
but still allows building for both windows architectures, i386 and x64.
Changed how HAVE_NC_SERVER is set in R/netcdfWrite.R. It defaults to FALSE, which is
appropriate on windows systems.  If nc_server is available on unix-likes,
issue a sed command in configure.ac to change HAVE_NC_SERVER to TRUE.
Create an empty configure.win, which avoids a warning on windows builds,
but still allows building for both windows architectures, i386 and x64.