avifil32: Use chunksize specified by the chunk itself, avoids a noticable ticking sound heard when reading past the chunk boundary.

ntdll: Implement LdrQueryImageFileExecutionOptions and use it to retrieve the per-process global flag.

Contrary to the MSDN, you can 'create only' whilst using a previous value
(ie +-variable and [~];value). This breaks the install of an application
I was debugging who uses that throughout for all their variables. In
addition whilst adding some tests I've also cleaned up invalid prefix
syntax handling and semicolon removal if the original string is empty.

rpcrt4: Add structure definition for RPC AUTH3 packet and use the size of this on sending to fix authentication against native servers.

Also use the new size to validate incoming AUTH3 packets to be
consistent with native.