libsys: various updates

- move system calls for use by services from libminlib into libsys;
- move srv_fork(2) and srv_kill(2) from RS and into libsys;
- replace getprocnr(2) with sef_self(3);
- rename previous getnprocnr(2) to getprocnr(2);
- clean up getepinfo(2);
- change all libsys calls that used _syscall to use _taskcall, so as
  to avoid going through errno to pass errors; this is already how
  most calls work anyway, and many of the calls previously using
  _syscall were already assumed to return the actual error;
- initialize request messages to zero, for future compatibility
  (note that this does not include PCI calls, which are in need of a
  much bigger overhaul, nor kernel calls);
- clean up more of dead DS code as a side effect.

Change-Id: I8788f54c68598fcf58e23486e270c2d749780ebb

lib/libpuffs/glo.h

@@ -43,8 +43,6 @@ EXTERN gid_t caller_gid;
 
 EXTERN int req_nr;
 
-EXTERN endpoint_t SELF_E;
-
 EXTERN char user_path[PATH_MAX+1];  /* pathname to be processed */
 
 EXTERN dev_t fs_dev;              /* The device that is handled by this FS proc

lib/libpuffs/puffs.c

@@ -694,7 +694,6 @@ static void sef_local_startup()
 static int sef_cb_init_fresh(int type, sef_init_info_t *info)
 {
 /* Initialize the Minix file server. */
-  SELF_E = getprocnr();
   return(OK);
 }
 
@@ -769,7 +768,7 @@ static void reply(
 )
 {
   if (OK != send(who, m_out))    /* send the message */
-	lpuffs_debug("libpuffs(%d) was unable to send reply\n", SELF_E);
+	lpuffs_debug("libpuffs(%d) was unable to send reply\n", sef_self());
 
   last_request_transid = 0;
 }