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/remote.c

@@ -0,0 +1,69 @@
+#include "ioutil.h"
+#include "util.h"
+
+#include <stdlib.h>
+#include <sys/un.h>
+
+static const int max_response=1024;
+
+void print_response( const char * response )
+{
+	char * response_text;
+	FILE * out;
+	int exit_status;
+
+	NULLCHECK( response );
+
+	exit_status = atoi(response);
+	response_text = strchr( response, ':' );
+
+	FATAL_IF_NULL( response_text,
+			"Error parsing server response: '%s'", response );
+
+	out = exit_status > 0 ? stderr : stdout;
+	fprintf(out, "%s\n", response_text + 2);
+}
+
+void do_remote_command(char* command, char* socket_name, int argc, char** argv)
+{
+	char newline=10;
+	int i;
+	debug( "connecting to run remote command %s", command );
+	int remote = socket(AF_UNIX, SOCK_STREAM, 0);
+	struct sockaddr_un address;
+	char response[max_response];
+
+	memset(&address, 0, sizeof(address));
+
+	FATAL_IF_NEGATIVE(remote, "Couldn't create client socket");
+
+	address.sun_family = AF_UNIX;
+	strncpy(address.sun_path, socket_name, sizeof(address.sun_path));
+
+	FATAL_IF_NEGATIVE(
+		connect(remote, (struct sockaddr*) &address, sizeof(address)),
+		"Couldn't connect to %s", socket_name
+	);
+
+	write(remote, command, strlen(command));
+	write(remote, &newline, 1);
+	for (i=0; i<argc; i++) {
+		if ( NULL != argv[i] ) {
+			write(remote, argv[i], strlen(argv[i]));
+		}
+		write(remote, &newline, 1);
+	}
+	write(remote, &newline, 1);
+
+	FATAL_IF_NEGATIVE(
+		read_until_newline(remote, response, max_response),
+		"Couldn't read response from %s", socket_name
+	);
+
+	print_response( response );
+
+	exit(atoi(response));
+
+	close(remote);
+}
+