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/libsys/sched_start.c

@@ -2,6 +2,7 @@
 #include <assert.h>
 #include <machine/archtypes.h>
 #include <minix/timers.h>
+#include <string.h>
 
 #include "kernel/config.h"
 #include "kernel/const.h"
@@ -23,7 +24,8 @@ int sched_inherit(endpoint_t scheduler_e,
 	assert(_ENDPOINT_P(parent_e) >= 0);
 	assert(maxprio < NR_SCHED_QUEUES);
 	assert(newscheduler_e);
-	
+
+	memset(&m, 0, sizeof(m));
 	m.SCHEDULING_ENDPOINT	= schedulee_e;
 	m.SCHEDULING_PARENT	= parent_e;
 	m.SCHEDULING_MAXPRIO	= (int) maxprio;
@@ -79,6 +81,7 @@ int sched_start(endpoint_t scheduler_e,
 	}
 
 	/* A user-space scheduler must schedule this process. */
+	memset(&m, 0, sizeof(m));
 	m.SCHEDULING_ENDPOINT	= schedulee_e;
 	m.SCHEDULING_PARENT	= parent_e;
 	m.SCHEDULING_MAXPRIO	= (int) maxprio;