DO NOT MERGE MTP: Add extended operations to support in-place editing of files

MTP does not support partial writes of files (the entire file must be transferred at once).
This makes it impossible to implement a FUSE file system for MTP
with acceptable performance.
To fix this problem, this change adds extended MTP operations to allow
partial writes to files:

SendPartialObject - allows writing a subset of a file, or appending to the end of a file

TruncateObject - allows changing the size of a file

BeginEditObject - must be called before using SendPartialObject and TruncateObject

EndEditObject - commits changes to a file after it has been edited with SendPartialObject or TruncateObject

We also add GetPartialObject64, which is the same as GetPartialObject
but has a 64 bit offset rather than 32.

Change-Id: Id5365e1c4dc55a2d819c16c9db0a3ac2260f9309
Signed-off-by: Mike Lockwood <lockwood@android.com>