Add flag for retaining layout version

Needed on Sony mint (Xperia T) as the /data/media folder is a
separate partition and normal data media wiping is not appropriate
for this device but the layout version file needs to be retained
for Android 4.2 multi-user.
diff --git a/partitions.hpp b/partitions.hpp
index 7660b8b..47436b0 100644
--- a/partitions.hpp
+++ b/partitions.hpp
@@ -107,6 +107,7 @@
 	string Fstab_File_System;                                                 // File system from the recovery.fstab
 	int Format_Block_Size;                                                    // Block size for formatting
 	bool Ignore_Blkid;                                                        // Ignore blkid results due to superblocks lying to us on certain devices / partitions
+	bool Retain_Layout_Version;                                               // Retains the .layout_version file during a wipe (needed on devices like Sony Xperia T where /data and /data/media are separate partitions)
 #ifdef TW_INCLUDE_CRYPTO_SAMSUNG
 	string EcryptFS_Password;                                                 // Have to store the encryption password to remount
 #endif