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

include/minix/syslib.h

@@ -26,7 +26,6 @@ struct rusage;
  *==========================================================================*/ 
 int _taskcall(endpoint_t who, int syscallnr, message *msgptr);
 int _kernel_call(int syscallnr, message *msgptr);
-int _sendcall(endpoint_t who, int type, message *msgptr);
 
 int sys_abort(int how);
 int sys_enable_iop(endpoint_t proc_ep);
@@ -261,5 +260,16 @@ int sys_setmcontext(endpoint_t proc, mcontext_t *mcp);
 /* input */
 int tty_input_inject(int type, int code, int val);
 
+/* Miscellaneous calls from servers and drivers. */
+pid_t srv_fork(uid_t reuid, gid_t regid);
+int srv_kill(pid_t pid, int sig);
+int getprocnr(pid_t pid, endpoint_t *proc_ep);
+int mapdriver(char *label, devmajor_t major);
+pid_t getnpid(endpoint_t proc_ep);
+uid_t getnuid(endpoint_t proc_ep);
+gid_t getngid(endpoint_t proc_ep);
+int checkperms(endpoint_t endpt, char *path, size_t size);
+int copyfd(endpoint_t endpt, int fd, int what);
+
 #endif /* _SYSLIB_H */