Support encrypted backup files

Also includes features merged from:

Update twrpTar by kokotas

Revised function entryExists().
Added function to get archive's uncompressed size.
Added option to exclude item(s) from the archive.
Revised forks()

Change-Id: I01fa2c81643161984eff2625247af75990684bd9
diff --git a/variables.h b/variables.h
index 4654703..ddae2af 100644
--- a/variables.h
+++ b/variables.h
@@ -166,6 +166,7 @@
 // Max archive size for tar backups before we split (1.5GB)
 #define MAX_ARCHIVE_SIZE 1610612736LLU
+//#define MAX_ARCHIVE_SIZE 52428800LLU // 50MB split for testing
 #define CUSTOM_LUN_FILE "/sys/devices/platform/usb_mass_storage/lun%d/file"