Add package for netcat

This adds GNU netcat (0.7.1). netcat is a utility for managing network connections.

Tested sucessfully on Samsung Chromebook 3 (XE500C13-K01US).

packages/nc.rb

+require 'package'
+
+class Nc < Package
+  version '0.7.1'
+  source_url 'http://downloads.sourceforge.net/project/netcat/netcat/0.7.1/netcat-0.7.1.tar.gz'
+  source_sha1 'b5cbc52a7ceed2fd5c4f5081f5747130b2d0fe01'
+ 
+  def self.build
+    system "./configure --prefix=/usr/local"
+    system "make"
+  end
+
+  def self.install
+    system "make", "DESTDIR=#{CREW_DEST_DIR}", "install"
+  end
+end