winebrowser: Add support for XTYP_REQUEST in DDE callback.

[Misha Koshelev]

IExplore on Windows supports the WWW_OpenURL topic as either an execute string or request
(this is required for at least one menu option in Vector NTI, also per my own testing with a little
program, and also http://support.microsoft.com/kb/q160957/ has more info on this than you'll
want to know). Only the execute string is used by ShellExecute, but other progs (e.g., Vector NTI)
seem to use the request as well. This adds support for that string.

I also renamed ddeExec to ddeString as this could either be the request or execute string in
this same patch. I hope it's not too confusing.

The -2 for acknowledgment is as on native and confirmed. The -3 for error I was not able to elicit
this error from native, but in any case since there is no "native" winebrowser I believe it is 
okay to return this when we encounter an error processing the DDE request (and, for example, a 
bad URL does not lead to a -3 per my tests). The DdeCreateDataHandle call, including all the 
parameters (CF_TEXT for a DWORD bugged me, but it is what native does; also the "Return" string
for the hsz) are as seen on WINEDEBUG=+ddeml using native iexplorer (running with the help of
ies4linux as I couldn't figure out how to start the darn thing in plain wine) with my little
program interrogating it.
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 programs/winebrowser/main.c |   54 ++++++++++++++++++++++++++++++------------
 1 files changed, 38 insertions(+), 16 deletions(-)
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