interactive: do strip trailing CRLF from input

interactive: do strip trailing CRLF from input

`git reset -p file` on a Windows CMD refuses to do anything useful
with this error message:

    (1/5) Unstage this hunk [y,n,q,a,d,j,J,g,/,e,p,?]? n
    'nly one letter is expected, got 'n

The letter 'O' at the beginning of the line is overwritten by an
apostrophe, so, clearly the parser sees the string "n\r".

strbuf_trim_trailing_newline() removes trailing CRLF from the string.
In particular, it first removes LF if present, and if that was the
case, it also removes CR if present.

git_read_line_interactively() clearly intends to remove CRLF as it
calls strbuf_trim_trailing_newline(). However, input is gathered using
strbuf_getline_lf(), which already removes the trailing LF. Now
strbuf_trim_trailing_newline() does not see LF, so that it does not
remove CR, either, and leaves it for the caller to process.

Call strbuf_getline() instead, which removes both LF and CR.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>