Fix email_classify.R under windows

[jnjcc]

email_classify.R failed on R 3.0.3, Win7 x64, with some error messages like:

Error in seq.default(which(text == "")[1] + 1, length(text), 1):
'from' cannot be NA, NaN or infinite

There were some similar errors in issue #4.

This patch removes the "open" parameter from file function, which happens to
solve the above error for me, although I don't understand why it worked yet.

I've tested this patch on R 3.1.1, Ubuntu 12.04, it produced the same result with or
without the "open" parameter for me.