oleaut32: preliminary support for VT_DISPATCH as parameters to VarAdd (and other 2-operand operations)

[Alex Villací­s Lasso]

This is a preliminary patch to add support for VT_DISPATCH as parameters 
to VarAdd and other arithmetic operations with variants. The tests still 
"pass" in the sense that null VT_DISPATCH as issued by the tests are 
still rejected. I post this in the hope that it will be reviewed while I 
prepare a test case.

Changelog:
* Add support for receiving of VT_DISPATCH parameters in several 
operator functions by fetching the result value, then reissuing the same 
operation on result data.

-- 
The following cryptic message was allegedly found in the inner edge of a Windows
XP installation CD:

4F6E65204F5320746F2072756C65207468656D20616C6C2C204F6E65204F5320746F2066696E6420
7468656D2C0D0A4F6E65204F5320746F206272696E67207468656D20616C6C20616E6420696E2074
6865206461726B6E6573732062696E64207468656D2E0A

It is rumored that only a true Unix Wizard can decypher this mysterious message,
which supposedly encodes the true nature and purpose of the software.