Changed pagefault delivery to VM

this patch changes the way pagefaults are delivered to VM. It adopts
the same model as the out-of-quantum messages sent by kernel to a
scheduler.

- everytime a userspace pagefault occurs, kernel creates a message
  which is sent to VM on behalf of the faulting process

- the process is blocked on delivery to VM in the standard IPC code
  instead of waiting in a spacial in-kernel queue (stack) and is not
  runnable until VM tell kernel that the pagefault is resolved and is
  free to clear the RTS_PAGEFAULT flag.

- VM does not need call kernel and poll the pagefault information
  which saves many (1/2?) calls and kernel calls that return "no more
  data"

- VM notification by kernel does not need to use signals

- each entry in proc table is by 12 bytes smaller (~3k save)

lib/libsys/sys_vmctl.c

@@ -12,22 +12,6 @@ PUBLIC int sys_vmctl(endpoint_t who, int param, u32_t value)
   return(r);
 }
 
-PUBLIC int sys_vmctl_get_pagefault_i386(endpoint_t *who, u32_t *cr2, u32_t *err)
-{
-  message m;
-  int r;
-
-  m.SVMCTL_WHO = SELF;
-  m.SVMCTL_PARAM = VMCTL_GET_PAGEFAULT;
-  r = _kernel_call(SYS_VMCTL, &m);
-  if(r == OK) {
-	*who = m.SVMCTL_PF_WHO;
-	*cr2 = m.SVMCTL_PF_I386_CR2;
-	*err = m.SVMCTL_PF_I386_ERR;
-  }
-  return(r);
-}
-
 PUBLIC int sys_vmctl_get_cr3_i386(endpoint_t who, u32_t *cr3)
 {
   message m;