top(1): chdir to / as init; remove unneeded comment

- chdir to / to allow unmounting of wd
- remove warning about running top(1) as setuid. If this is a concern we
should just drop privs instead.

usr.bin/top/machine.c

@@ -1613,11 +1613,6 @@ compare_ivcsw(const void *arg1, const void *arg2)
 /*
  * proc_owner(pid) - returns the uid that owns process "pid", or -1 if
  *		the process does not exist.
- *		It is EXTREMELY IMPORTANT that this function work correctly.
- *		If top runs setuid root (as in SVR4), then this function
- *		is the only thing that stands in the way of a serious
- *		security problem.  It validates requests for the "kill"
- *		and "renice" commands.
  */
 
 int

usr.bin/top/top.c

@@ -260,6 +260,15 @@ main(int argc, char *argv[])
 #define CMD_order	26
 #define CMD_pid		27
 
+    /*
+     * Since top(1) is often long running and
+     * doesn't typically care about where its running from
+     * chdir to the root to allow unmounting of its
+     * originall wd. Failure is alright as this is
+     * just a courtesy for users.
+     */
+    chdir("/");
+
     /* set the buffer for stdout */
 #ifdef DEBUG
     extern FILE *debug;