Allow filename prompt when saving multiple attachments to a directory. (closes #3083)

Currently, if you specify a directory when saving multiple attachments
and choose (a)ll, the first attachment is saved without confirming the
filename.  Subsequent attachments prompt for the filename.
version.sh: step back from $() to ``.  closes #3661
(grafted from 01cf5814dfe5e79b65b1d950aab1276d19a9f031)
Fix postpone/resume to not remove a Mail-Followup-To header  (closes #3070)

This solution changes mutt_prepare_template() to check whether the
message_id field is NULL to decide whether to wipe the message-id and
mail-followup-to headers when instantiating the message.

If we are resending a message, we don't want the previous message-id
and mail-followup-to headers.  If we are resuming a postponed message,
however, we want to keep the mail-followup-to header if any was set
before the postpone.
(grafted from d7d83298011a6e7aa31bde49e0b6b21209a85fd2)
only terminate the write-half of the TLS connection to avoid hanging if the remote doesn't respond.

RFC5246 section 7.2.4 states that the initiator of the closure need not wait for the remote to response before closing the read-half.

closes #3633
return 0 if import of cert failed to match other error conditions.
Display the KeyID when the pubkey is not found in the user's keyring during signature verification.

closes #3654
use LOFF_T as the type for variables used in fseeko()

closes #3487
Ensure that at least one signature was generated to catch the case where $pgp_sign_as is unset and no default key is specified in ~/.gnupg/gpg.conf

closes #3658
When recalling a postponed message that does not have a x-mutt-fcc header
field, generate a default FCC just as we do for new messages.  If x-mutt-fcc is
present but empty, we assume that means the user does not want a copy.

closes #3653
create stable branch
Move HEAD to default
Merge stable into default
merge changesets from stable branch
remove trailing period from documentation for $pgp_list_pubring_command
remove trailing period from documentation for $pgp_list_secring_command
Merge stable into default