Adding e4crypt support

Redirect all crypto calls to e4crypt equivalents if file level encryption
detected. Note this change implements only the ones needed for minimal
functionality.

Requires matching change:
  https://googleplex-android-review.git.corp.google.com/#/c/642778/

Change-Id: I622d1a91704de4b3ab655486e6d38cd6718e6016
diff --git a/cryptfs.h b/cryptfs.h
index a8b2e45..c34410a 100644
--- a/cryptfs.h
+++ b/cryptfs.h
@@ -240,7 +240,7 @@
   int cryptfs_setfield(const char *fieldname, const char *value);
   int cryptfs_mount_default_encrypted(void);
   int cryptfs_get_password_type(void);
-  char* cryptfs_get_password(void);
+  const char* cryptfs_get_password(void);
   void cryptfs_clear_password(void);
 #ifdef __cplusplus
 }