Split urlmon into XP and Vista versions

Currently, our URLMON has exports of Vista and XP. This causes confusions to apps seeing we export one function and then goes to Vista + mode and tried to load function we don't export and it fails. I was trying to run a version of Windows Movie Maker from XP (I won't post the link) that was made portable that tried to call CompatFlagsFromClsid which appears to be Vista and newer. The app works fine in XP with the default urlmon.

This might have to be something like we did with kernel32 and kernel32_vista. However, I fear that we don't have enough man power to do this.