contrib/thunderbird-patch-inline: do not require bash to run the script

contrib/thunderbird-patch-inline: do not require bash to run the script

The script does not have to be run under bash, but any POSIX compliant
shell would do, as it does not use any bash-isms.

It may be written under a different style than what is recommended in
Documentation/CodingGuidelines, but that is a different matter.

While at it, fix obvious typos in the comment.

Signed-off-by: Maxin B. John <maxin@maxinbjohn.info>
Signed-off-by: Junio C Hamano <gitster@pobox.com>