git with XCode and ignoring .xcodeproj on merge?

I'm getting up to speed on us开发者_如何学JAVAing git with XCode but have run into a situation that I'm not quite sure how to handle.

I have a branch of my project "branchA" that has a build target base SDK of iOS 3.2

I have "branchB" that has been forked from branchA that has a build target base SDK for iOS4.2

I'm continuing with development on both branches, branchA with functionality that doesn't depend on SDK4.2 features, branchB for those features that do depend on 4.2

From time to time, I want to merge the changes made in branchA into branchB.

This of course results in some conflicts that I can easily correct -- except those that occur in the .xcodeproj file

How can I tell git not to merge the .xcodeproj file from branchA into branchB -- in essence, keep the .xcodproj file in branchB and ignore any differences it may have with branchA?

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As I detail in this SO answer, you can use

• a merge driver with a keepmine script.
• or a git rerere to record one merge resolution and keep re-applying it.