Allow a file to have a separate 'Item type' attribute for each build configuration
At the moment the 'Item type' of a file is set in it Properties page, and rather confusingly this is under the 'Configuration Properties' section.
In actual fact this setting cannot be set for only one configuration. Changing it in one changes it for all.
However there are cases where users would like a file to be treated as, say, a header under one configuration, but a source file under another.