Switch from a rake-based build to a make-based build.

This commit beefs up the Makefile to do the build, instead of the
Rakefile.

It also removes from the Rakefile the dependency on rake_utils, which
should mean it's ok to build in a schroot.

The files are reorganised to make the Makefile rules more tractable,
although the reorganisation reveals a problem with our current code
organisation.

The problem is that the proxy-specific code transitively depends on the
server code via flexnbd.h, which has a circular dependency on the server
and client structs. This should be broken in a future commit by
separating the flexnbd struct into a shared config struct and
server-specific parts, so that the server code can be moved into
src/server to more accurately show the functional dependencies.

tests/acceptance/test_happy_path.rb

@@ -2,12 +2,17 @@
 
 require 'test/unit'
 require 'environment'
+require 'flexnbd/constants'
 
 class TestHappyPath < Test::Unit::TestCase
   def setup
     @env = Environment.new
   end
 
+  def bin(str)
+    FlexNBD.binary str
+  end
+
   def teardown
     @env.nbd1.can_die(0)
     @env.nbd2.can_die(0)
@@ -22,13 +27,13 @@ class TestHappyPath < Test::Unit::TestCase
     [0, 12, 63].each do |num|
 
       assert_equal(
-        @env.nbd1.read(num*@env.blocksize, @env.blocksize),
-        @env.file1.read(num*@env.blocksize, @env.blocksize)
+        bin( @env.nbd1.read(num*@env.blocksize, @env.blocksize) ),
+        bin( @env.file1.read(num*@env.blocksize, @env.blocksize) )
       )
     end
 
     [124, 1200, 10028, 25488].each do |num|
-      assert_equal(@env.nbd1.read(num, 4), @env.file1.read(num, 4))
+      assert_equal(bin(@env.nbd1.read(num, 4)), bin(@env.file1.read(num, 4)))
     end
   end