Fix the git tests on Appveyor
Fix the git tests on Appveyor

We must configure git to ignore the file mode, or else it will checkout the
tree with the executable files with the wrong mode, leaving it in a "dirty"
state. See
https://stackoverflow.com/questions/1580596/how-do-i-make-git-ignore-file-mode-chmod-changes.

rmcgibbo/conda-build,dan-blanchard/conda-build,ilastik/conda-build,rmcgibbo/conda-build,ilastik/conda-build,frol/conda-build,sandhujasmine/conda-build,ilastik/conda-build,mwcraig/conda-build,frol/conda-build,sandhujasmine/conda-build,frol/conda-build,rmcgibbo/conda-build,sandhujasmine/conda-build,dan-blanchard/conda-build,mwcraig/conda-build,mwcraig/conda-build,dan-blanchard/conda-build