add unzip package

upstream code isn't maintained any more, many distros have unofficial
patch sets, so we use the full ubuntu patch set.  Includes several
security vulnerabilities

packages/unzip.rb

+require 'package'
+
+class Unzip < Package
+  version '1.6_1'
+  source_url 'https://downloads.sourceforge.net/project/infozip/UnZip%206.x%20%28latest%29/UnZip%206.0/unzip60.tar.gz'
+  source_sha1 'abf7de8a4018a983590ed6f5cbd990d4740f8a22'
+  depends_on 'patch'
+
+  # adapted from the homebrew recipe as seen at: https://github.com/Homebrew/homebrew-dupes/blob/master/unzip.rb
+  # Upstream is unmaintained so we use the Ubuntu unzip-6.0-20ubuntu1 patchset:
+  # http://changelogs.ubuntu.com/changelogs/pool/main/u/unzip/unzip_6.0-20ubuntu1/changelog
+  def self.patch
+    patch_url = "https://launchpad.net/ubuntu/+archive/primary/+files/unzip_6.0-20ubuntu1.debian.tar.xz"
+    patch_sha256 = "0ddf122ef15b739e3ea06db4b9e80f40759dce23a2c886678881453a43bd0842"
+
+    system('wget', '--continue', '--no-check-certificate', patch_url, '-O', 'unzippatches.tar.xz')
+    abort 'Checksum mismatch :/ try again' unless Digest::SHA256.hexdigest( File.read("./unzippatches.tar.xz") ) == patch_sha256
+    system("tar","-xf","unzippatches.tar.xz")
+
+    system("for i in `cat debian/patches/series`; do  patch -p 1 < debian/patches/$i; done")
+  end
+
+  def self.build
+    self.patch
+    system "make -f unix/Makefile generic"
+  end
+
+  def self.install
+    system "make", "DESTDIR=#{CREW_DEST_DIR}", "-f", "unix/Makefile", "install"
+  end
+
+end