Return daap.songalbumid as a hash of the album_artist + album

iPhone remote will later want to query by album. Instead of doing a
fulltext query, it uses a 64-bit hash of the album + album_artist. It
is not necessary to use the same hash algorithm that iTunes uses. The
important thing is that we can later respond to a query=('daap.songalbumid:xxx')
with this value.

src/httpd_daap.c

@@ -33,6 +33,7 @@
 #include <regex.h>
 #include <limits.h>
 #include <stdint.h>
+#include <inttypes.h>
 
 #include <event.h>
 #include "evhttp/evhttp.h"
@@ -175,6 +176,8 @@ static struct dmap_field_map dmap_fields[] =
       -1,                                 -1 },
     { 0, DMAP_TYPE_STRING,  "asal", "daap.songalbum",
       dbmfi_offsetof(album),              -1 },
+    { 0, DMAP_TYPE_LONG,    "asai", "daap.songalbumid",  /* special case; will be transformed to LONG (hash) */
+      dbmfi_offsetof(album),              -1 },
     { 0, DMAP_TYPE_STRING,  "asar", "daap.songartist",
       dbmfi_offsetof(artist),             -1 },
     { 0, DMAP_TYPE_SHORT,   "asbt", "daap.songbeatsperminute",
@@ -960,6 +963,7 @@ daap_reply_songlist_generic(struct evhttp_request *req, struct evbuffer *evbuf,
   char **strval;
   char *ptr;
   uint32_t *meta;
+  int64_t songalbumid;
   int nmeta;
   int nsongs;
   int transcode;
@@ -1153,6 +1157,19 @@ daap_reply_songlist_generic(struct evhttp_request *req, struct evbuffer *evbuf,
 	      continue;
 	    }
 
+	  /* Special handling for songalbumid (asai)
+	   * Return an int64_t hash of the album_artist & album
+	   */
+	  if (strcmp(dfm->tag, "asai") == 0)
+	    {
+	      songalbumid = daap_songalbumid(dbmfi.album_artist, dbmfi.album);
+
+	      dmap_add_long(song, dfm->tag, songalbumid);
+
+	      DPRINTF(E_DBG, L_DAAP, "Generated meta tag %s (%" PRIi64 ") based on (%s,%s)\n", dfm->desc, songalbumid, dbmfi.album_artist, dbmfi.album);
+	      continue;
+	    }
+
 	  if (transcode)
             {
               switch (dfm->mfi_offset)