
In get_token, edges 61, 63, 79, 81 all follow on
  unget_char returning EOF, which it does only if its
  call to ungetc fails; don't know how to make ungetc
  fail on these branches.

  Edge 51 follows on unget_char not returning EOF in
  a case where it necessarilty returns EOF (from trying
  to ungetc EOF), so it can't be exercised.
