How to make git ignore a directory while merging

I don't actually use Git, but I think this would work for your case:

Use something like what's specified here: https://gist.github.com/564416

git checkout master    
git merge --no-commit --no-ff development
git reset -- /path/to/folder # revert updates from path
git commit

Again, I don't use git, I am just deferring to how I think things work based on my experience with TryGit.

1. checkout master
2. merge, but don't commit, no fast forward.
3. merges are now staged, so reset that entire directory tree
4. commit