Fix bug #167 - Build errors on OpenBSD.

- Don't link with -ldl, as it is not needed in most cases
- Don't compile plugins if USE_PLUGINS=NO
- Fix warning about missing newline at end of getopt.h
- Removed the O_NOATIME open() flag from the logging plugin.
- Removed the O_LARGEFILE open() flag. _FILE_OFFSET_BITS is 64.
- Use fsync() if fdatasync() is not available for log file writing.
- Replaced some sprintf() with snprintf() due to compiler warnings (though, they were length limited otherwise).
- Replaced two occurences of strcpy() with memcpy().

src/util/misc.c

@@ -399,7 +399,7 @@ const char* get_timestamp(time_t now)
 {
 	static char ts[32] = {0, };
 	struct tm* t  = localtime(&now);
-	sprintf(ts, "[%02d:%02d]", t->tm_hour, t->tm_min);
+	snprintf(ts, sizeof(ts), "[%02d:%02d]", t->tm_hour, t->tm_min);
 	return ts;
 }