libroot: sethostname() now uses ftruncate().

* Before, it would just overwrite the previous name, leaving extra
  bytes from the previous name (they wouldn't become part of the
  host name, but it just didn't look that nice).

src/system/libroot/posix/unistd/hostname.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2007, Axel Dörfler, [email protected]. All rights reserved.
+ * Copyright 2002-2014, Axel Dörfler, [email protected].
  * Distributed under the terms of the MIT License.
  */
 
@@ -46,6 +46,7 @@ sethostname(const char *hostName, size_t nameSize)
 		return -1;
 
 	nameSize = min_c(nameSize, MAXHOSTNAMELEN);
+	ftruncate(file, nameSize + 1);
 
 	if (write(file, hostName, nameSize) != (ssize_t)nameSize
 		|| write(file, "\n", 1) != 1) {