[NCF-286]/e-support:JVN-123940

using cygwin64 causes a couple of bugs during make check.
Fixes are as follows:
1. in ncdump.c and nccopy.c change all occurrences of
   'return EXIT_FAILURE'
   and
   'return EXIT_SUCCESS'
   with
   exit(EXIT_FAILURE)
   and
   exit(EXIT_SUCCESS)
   respectively.
   I have no idea why this works.
2. in libdap2/ncdap3a.c#freeNCDAPCOMMON,
   remove the call to nc_abort, it is
   causing a loop; not sure why this
   is not caught under other operating systems.
Merge branch 'master' of http://github.com/Unidata/netcdf-c