CC-2977: Never delete files from the database

- using mtab(previous and current) files to figure out directories to be
added or removed
- adding index to cc_files
- see the tickets and media monitor design page for more info

airtime_mvc/build/sql/schema.sql

@@ -43,7 +43,7 @@ CREATE TABLE "cc_music_dirs"
 	"directory" TEXT,
 	"type" VARCHAR(255),
 	"exists" BOOLEAN default 't',
-	"removed" BOOLEAN default 'f',
+	"watched" BOOLEAN default 't',
 	PRIMARY KEY ("id"),
 	CONSTRAINT "cc_music_dir_unique" UNIQUE ("directory")
 );
@@ -118,7 +118,7 @@ CREATE TABLE "cc_files"
 	"subject" VARCHAR(512),
 	"contributor" VARCHAR(512),
 	"language" VARCHAR(512),
-	"file_exist" BOOLEAN default 't',
+	"file_exists" BOOLEAN default 't',
 	"soundcloud_id" INTEGER,
 	"soundcloud_error_code" INTEGER,
 	"soundcloud_error_msg" VARCHAR(512),
@@ -135,6 +135,8 @@ CREATE INDEX "cc_files_md5_idx" ON "cc_files" ("md5");
 
 CREATE INDEX "cc_files_name_idx" ON "cc_files" ("name");
 
+CREATE INDEX "cc_files_file_exists_idx" ON "cc_files" ("file_exists");
+
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 -- cc_perms
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