new test modules

[Bruno Haible]

Hi,

I added minimal tests for the modules
  arpa_inet
  byteswap
  fcntl
  inttypes
  netinet_in
  stdbool
  string
  sys_select
  sys_socket
  sys_stat
  sys_time
  sysexits
  time
  unistd
  wchar
  wctype 

Just to check that the include file that it defines can really be included.

Feel free to add more checks to these tests when you have time.

Bruno