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/util.c

@@ -0,0 +1,87 @@
+#include <stdarg.h>
+#include <stdio.h>
+#include <pthread.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <malloc.h>
+#include <unistd.h>
+#include <time.h>
+
+#include "util.h"
+
+pthread_key_t cleanup_handler_key;
+
+int log_level = 2;
+
+void error_init(void)
+{
+	pthread_key_create(&cleanup_handler_key, free);
+}
+
+void error_handler(int fatal)
+{
+	DECLARE_ERROR_CONTEXT(context);
+
+	if (context) {
+		longjmp(context->jmp, fatal ? 1 : 2 );
+	}
+	else {
+		if ( fatal ) { abort(); }
+		else { pthread_exit((void*) 1); }
+	}
+}
+
+
+void exit_err( const char *msg )
+{
+	fprintf( stderr, "%s\n", msg );
+	exit( 1 );
+}
+
+
+void mylog(int line_level, const char* format, ...)
+{
+	if (line_level < log_level) { return; }
+
+	va_list argptr;
+
+	va_start(argptr, format);
+	vfprintf(stderr, format, argptr);
+	va_end(argptr);
+}
+
+uint64_t monotonic_time_ms()
+{
+	struct timespec ts;
+	uint64_t seconds_ms, nanoseconds_ms;
+
+	FATAL_IF_NEGATIVE(
+		clock_gettime(CLOCK_MONOTONIC, &ts),
+		SHOW_ERRNO( "clock_gettime failed" )
+	);
+
+	seconds_ms = ts.tv_sec;
+	seconds_ms = seconds_ms * 1000;
+
+	nanoseconds_ms = ts.tv_nsec;
+	nanoseconds_ms = nanoseconds_ms / 1000000;
+
+	return seconds_ms + nanoseconds_ms;
+}
+
+
+void* xrealloc(void* ptr, size_t size)
+{
+	void* p = realloc(ptr, size);
+	FATAL_IF_NULL(p, "couldn't xrealloc %d bytes", ptr ? "realloc" : "malloc", size);
+	return p;
+}
+
+void* xmalloc(size_t size)
+{
+	void* p = xrealloc(NULL, size);
+	memset(p, 0, size);
+	return p;
+}
+