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.

src/common/self_pipe.h

@@ -0,0 +1,19 @@
+#ifndef SELF_PIPE_H
+#define SELF_PIPE_H
+
+#include <sys/select.h>
+
+struct self_pipe {
+	int read_fd;
+	int write_fd;
+};
+
+
+struct self_pipe * self_pipe_create(void);
+int self_pipe_signal( struct self_pipe * sig );
+int self_pipe_signal_clear( struct self_pipe *sig );
+int self_pipe_destroy( struct self_pipe * sig );
+int self_pipe_fd_set( struct self_pipe * sig, fd_set * fds );
+int self_pipe_fd_isset( struct self_pipe *sig, fd_set *fds );
+
+#endif