FYI: A plain git reset cleans the index -- now the spurious file isn't listed in the index or working dir:
[gitx-test (master)]$ git reset
Unstaged changes after reset:
M goodbye.txt
M hello.txt
[gitx-test (master)]$ git status
# On branch master
# Changes not staged for commit:
# (use "git add <file>..." to update what will be committed)
# (use "git checkout -- <file>..." to discard changes in working
directory)
#
# modified: goodbye.txt
# modified: hello.txt
#
