Fixed deprecation warnings while Nim compiles.

I just removed unsigned and changed a writeLn() call to writeLine() to
avoid the remaining deprecation warnings.

lib/impure/rdstdin.nim

@@ -100,7 +100,7 @@ when defined(Windows):
     stdout.write "\n"
 
 else:
-  import linenoise, termios, unsigned
+  import linenoise, termios
 
   proc readLineFromStdin*(prompt: string): TaintedString {.
                           tags: [ReadIOEffect, WriteIOEffect].} =

lib/pure/nativesockets.nim

@@ -12,7 +12,7 @@
 
 # TODO: Clean up the exports a bit and everything else in general.
 
-import unsigned, os
+import os
 
 when hostOS == "solaris":
   {.passl: "-lsocket -lnsl".}

lib/pure/net.nim

@@ -10,7 +10,7 @@
 ## This module implements a high-level cross-platform sockets interface.
 
 {.deadCodeElim: on.}
-import nativesockets, os, strutils, unsigned, parseutils, times
+import nativesockets, os, strutils, parseutils, times
 export Port, `$`, `==`
 
 const useWinVersion = defined(Windows) or defined(nimdoc)

lib/pure/securehash.nim

@@ -7,8 +7,7 @@
 #    distribution, for details about the copyright.
 #
 
-import
-  strutils, unsigned
+import strutils
 
 const Sha1DigestSize = 20