Add porcelain command to revert a single staged file to its HEAD state while preserving its staged state

Hi,

I have been looking for such a command/option and no one gave me
sufficient answer. So this message should be considered as a feature
request. I had a situation where I had staged a file with a problem
solution in it, then I wanted to experiment with a different solution
so I had to revert the file to its HEAD state and I couldn't find a
way that preserves the staged state of that file. More discussions:

https://groups.google.com/forum/?fromgroups=#!topic/git-users/nYiN-rE_3i0

http://stackoverflow.com/questions/16335799/git-porcelain-command-to-revert-a-single-file-to-its-head-state-but-keep-its-sta

Regards,
Dimitar Bonev