chainlint: recognize multi-line quoted strings more robustly

chainlint: recognize multi-line quoted strings more robustly

chainlint.sed recognizes multi-line quoted strings within subshells:

    echo "abc
        def" >out &&

so it can avoid incorrectly classifying lines internal to the string as
breaking the &&-chain. To identify the first line of a multi-line
string, it checks if the line contains a single quote. However, this is
fragile and can be easily fooled by a line containing multiple strings:

    echo "xyz" "abc
        def" >out &&

Make detection more robust by checking for an odd number of quotes
rather than only a single one.

(Escaped quotes are not handled, but support may be added later.)

The original multi-line string recognizer rather cavalierly threw away
all but the final quote, whereas the new one is careful to retain all
quotes, so the "expected" output of a couple existing chainlint tests is
updated to account for this new behavior.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>