git blame crashes with internal error

Hi Junio,

git blame just decided to crash on me, when I tried to use it while
resolving a merge conflict. Interesting is probably, that it crashes
when given the filename of a file that is not _directly_ affected by the
merge, but contains code that originates from a file that caused
conlicts.

Error message is:
fatal: internal error: ce_mode is 0

I tried all git releases from 1.5.3 to 1.5.3.4 as well as the current
master and all of them crashed. A small shell script to reproduce the
problem is attached.

Thanks,
Björn