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

kernel/extract-mfield.sh

@@ -5,7 +5,7 @@ set -e
 find_files_and_lines()
 (
 	find  ../lib/libc/sys-minix ../lib/libsys -name '*.c' | \
-	xargs egrep -n '((_sendcall|_syscall|_taskcall)\([^,][^,]*,[ 	]*|_kernel_call\()[A-Z_][A-Z0-9_]*,[ 	]*&m\)' | \
+	xargs egrep -n '((_syscall|_taskcall)\([^,][^,]*,[ 	]*|_kernel_call\()[A-Z_][A-Z0-9_]*,[ 	]*&m\)' | \
 	cut -d: -f1,2
 )