Git has bad performance when traversing change-sets with large PPM files

Steps to reproduce:

1. Create a new git repo and add a 640x480 PPM image in ASCII format
2. Add a .gitattributes file with the line "*.ppm binary"
3. Commit the PPM file
4. Change the PPM image's contents
5. Add and commit
6. Try to do a git rebase -i to the initial commit
7. Watch the CPU peg at 100%

I'm using git version 1.6.3.3

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Thanks,