[db] Move database upgrade logic to separate file

src/Makefile.am

@@ -71,6 +71,7 @@ forked_daapd_LDADD = -lrt \
 
 forked_daapd_SOURCES = main.c \
 	db.c db.h \
+	db_upgrade.c db_upgrade.h \
 	logger.c logger.h \
 	conffile.c conffile.h \
 	cache.c cache.h \

src/db_upgrade.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2015 Christian Meffert <christian.meffert@googlemail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#ifndef SRC_DB_UPGRADE_H_
+#define SRC_DB_UPGRADE_H_
+
+#include <sqlite3.h>
+
+int
+db_upgrade(sqlite3 *hdl, int db_ver);
+
+#endif /* SRC_DB_UPGRADE_H_ */