Fix line numbers when the input contains multiple sequential \n characters.

[cscott]

For example, the input \r\n\n\r should represent three new lines. But:

> text = '\r\n\n\r'
> text.replace(/(\r|\n){1,2}/g, "\n");  // previous code says this is only two newlines
'\n\n'
> text.replace(/(\r\n?|\n)/g, "\n"); // this patch returns three, as expected.
'\n\n\n'

This PR fixes issue #155.