Changed tests and tools to use 'discard' statements instead of 'nil' for empty blocks.

tests/overload/toverwr.nim

@@ -1,13 +1,13 @@
-discard """
-  file: "toverwr.nim"
-  output: "hello"
-"""
+discard """
+  file: "toverwr.nim"
+  output: "hello"
+"""
 # Test the overloading resolution in connection with a qualifier
 
 proc write(t: TFile, s: string) =
-  nil # a nop
+  discard # a nop
 
 system.write(stdout, "hello")
 #OUT hello
-
-
+
+