kakasi: avoid an implicit declaration of exit.

This caused the following false alarm:

```
error: can not use EUC-JP or UTF-8 encoding on iconv
```

See https://git.launchpad.net/ubuntu/+source/kakasi/commit/?h=applied/ubuntu/plucky&id=08f53a5.

pkgs/by-name/ka/kakasi/avoid-an-implicit-declaration-of-exit.patch

@@ -0,0 +1,13 @@
+diff --git a/configure b/configure
+index b4bd9ef..0e0df9d 100755
+--- a/configure
++++ b/configure
+@@ -12557,7 +12557,7 @@ else
+ int
+ main ()
+ {
+-if (iconv_open("EUC-JP", "UTF-8") == -1) exit(1);
++if (iconv_open("EUC-JP", "UTF-8") == -1) return 1;
+   ;
+   return 0;
+ }

pkgs/by-name/ka/kakasi/package.nix

@@ -28,6 +28,8 @@ stdenv.mkDerivation rec {
     sha256 = "1qry3xqb83pjgxp3my8b1sy77z4f0893h73ldrvdaky70cdppr9f";
   };
 
+  patches = [ ./avoid-an-implicit-declaration-of-exit.patch ];
+
   postPatch = ''
     for a in tests/kakasi-* ; do
       substituteInPlace $a \