Rather than replacing the configured subject prefix (either through the
git config or command line) entirely with "RFC PATCH", this change
prepends RFC to whatever subject prefix was already in use.

This is useful, for example, when a user is working on a repository that
has a subject prefix considered to disambiguate patches:

	git config format.subjectPrefix 'PATCH my-project'

Prior to this change, formatting patches with --rfc would lose the
'my-project' information.

The data flow for the subject-prefix was that rev.subject_prefix
were to be kept the authoritative version of the subject prefix even
while parsing command line options, and sprefix variable was used as
a temporary area to futz with it.  Now, the parsing code has been
refactored to build the subject prefix into the sprefix variable and
assigns its value at the end to rev.subject_prefix, which makes the
flow easier to grasp.

Signed-off-by: Drew DeVault <sir@cmpwn.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

While help.autocorrect can be set to 0 to decline auto-execution of
possibly mistyped commands, it still spends cycles to compute the
suggestions, and it wastes screen real estate.

Update help.autocorrect to accept the string "never" to just exit
with error upon mistyped commands to help users who prefer to never
see suggested corrections at all.

While at it, introduce "immediate" as a more readable way to
immediately execute the auto-corrected command, which can be done
with negative value.

Signed-off-by: Drew DeVault <sir@cmpwn.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

I've seen several people mis-configure git send-email on their first
attempt because they set the sendmail.* config options - not
sendemail.*. This patch detects this mistake and bails out with a
friendly warning.

Signed-off-by: Drew DeVault <sir@cmpwn.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

When shown the email summary, an opportunity is presented for the user
to edit the email as if they had specified --annotate. This also permits
them to edit it multiple times.

Signed-off-by: Drew DeVault <sir@cmpwn.com>
Reviewed-by: Simon Ser <contact@emersion.fr>
Helped-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>