Use comments to split aof.c into sections.

This makes the code more readable, it is still not the case to split the
file itself into three different files, but the logical separation
improves the readability especially since new commits are going to
introduce an additional section.

src/aof.c

@@ -12,6 +12,12 @@
 
 void aofUpdateCurrentSize(void);
 
+/* ----------------------------------------------------------------------------
+ * AOF file implementation
+ * ------------------------------------------------------------------------- */
+
+/* Starts a background task that performs fsync() against the specified
+ * file descriptor (the one of the AOF file) in another thread. */
 void aof_background_fsync(int fd) {
     bioCreateBackgroundJob(REDIS_BIO_AOF_FSYNC,(void*)(long)fd,NULL,NULL);
 }
@@ -280,6 +286,10 @@ void feedAppendOnlyFile(struct redisCommand *cmd, int dictid, robj **argv, int a
     sdsfree(buf);
 }
 
+/* ----------------------------------------------------------------------------
+ * AOF loading
+ * ------------------------------------------------------------------------- */
+
 /* In Redis commands are always executed in the context of a client, so in
  * order to load the append only file we need to create a fake client. */
 struct redisClient *createFakeClient(void) {
@@ -424,6 +434,10 @@ fmterr:
     exit(1);
 }
 
+/* ----------------------------------------------------------------------------
+ * AOF rewrite
+ * ------------------------------------------------------------------------- */
+
 /* Delegate writing an object to writing a bulk string or bulk long long.
  * This is not placed in rio.c since that adds the redis.h dependency. */
 int rioWriteBulkObject(rio *r, robj *obj) {