Fix bz2.rb symbolic link problem

Add check method
Correct the version number
Correct dependencies

packages/bz2.rb

 require 'package'
 
 class Bz2 < Package
-  version '1.4.17'
+  version '1.0.6'
   source_url 'http://www.bzip.org/1.0.6/bzip2-1.0.6.tar.gz'
   source_sha1 '3f89f861209ce81a6bab1fd1998c0ef311712002'
 
+  depends_on 'diffutils' => :build
+
   def self.build
     system "make -f Makefile-libbz2_so"
   end
 
   def self.install
+    # bz2 Makefile doesn't have DESTDIR, so we need several tricks
+    # to make it install files correctly.
+
+    # Modify Makefile from "ln -s $(PREFIX)/bin/xxx $(PREFIX)/bin/yyy" to
+    # "ln -s xxx $(PREFIX)/bin/yyy"
+    system "sed", "-i", "Makefile", "-e", "/ln -s/s:$(PREFIX)/bin/::"
+
+    # Use PREFIX instead of DESTDIR
     system "make", "PREFIX=#{CREW_DEST_DIR}/usr/local", "install"
   end
+
+  def self.check
+    system "make", "test"
+  end
 end