Fail if the command line input file cannot be opened
tree5f089f19e2b2fdbd131daeb2b61f79b2e96d82c2
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-rw-r--r-- 35 .gitignore
-rw-r--r-- 509 Makefile
-rw-r--r-- 16214 git-export-filter.c
-rw-r--r-- 16 git-export-help.txt