fix compilation in the presence of -Werror

  CC       node.o
node.c: In function 'rtrim':
node.c:248:2: error: C++ style comments are not allowed in ISO C90 [-Werror]
  // null-terminate new string
  ^
node.c:248:2: error: (this will be reported only once per input file) [-Werror]
node.c: In function 'handle_connection':
node.c:473:19: error: unused variable 'dp' [-Werror=unused-variable]
    struct dirent* dp;
                   ^
cc1: all warnings being treated as errors
make: *** [node.o] Error 1
use bool where appropriate

Avoids a splint warning about using int in a boolean context.
handle NULL pointers from get{pw,gr}nam
fixes for splint

 * Missing declarations of undefined or exposed storage.
 * Mixing of different types (non-bool <-> bool, integer sizes).
there usually is no group called "nobody"
verify that set[gu]id works
node: remove extra ";"