VM: full munmap

complete munmap implementation; single-page references made
a general munmap() implementation possible to write cleanly.

	. memory: let the MIOCRAMSIZE ioctl set the imgrd device
	  size (but only to 0)
	. let the ramdisk command set sizes to 0
	. use this command to set /dev/imgrd to 0 after mounting /usr
	  in /etc/rc, so the boot time ramdisk is freed (about 4MB
	  currently)

lib/libc/include/namespace.h

@@ -923,7 +923,6 @@
 #define writev _writev
 #define minix_mmap _minix_mmap
 #define minix_munmap _minix_munmap
-#define minix_munmap_text _minix_munmap_text
 #define vfork __vfork14
 #endif /* __minix */
 

lib/libc/sys-minix/mmap.c

@@ -12,7 +12,6 @@ __weak_alias(vm_getphys, _vm_getphys)
 __weak_alias(vm_getrefcount, _vm_getrefcount)
 __weak_alias(minix_mmap, _minix_mmap)
 __weak_alias(minix_munmap, _minix_munmap)
-__weak_alias(minix_munmap_text, _minix_munmap_text)
 #endif
 
 
@@ -65,16 +64,6 @@ int minix_munmap(void *addr, size_t len)
 }
 
 
-int minix_munmap_text(void *addr, size_t len)
-{
-	message m;
-
-	m.VMUM_ADDR = addr;
-	m.VMUM_LEN = len;
-
-	return _syscall(VM_PROC_NR, VM_MUNMAP_TEXT, &m);
-}
-
 void *vm_remap(endpoint_t d,
 			endpoint_t s,
 			void *da,