mbox: remove sup-sync-back-mbox
Fix attachment filename handling

Attachment#write_to_disk created its temporary file with a shell-escaped name.
Passing the path to this file to write_to_disk's block parameter and returning
it created a double-escape problem, which rendered attachments with e.g. spaces
in the filename unusable.

Fixed by removing the use of the original filename from the tempfile name. Also
removed the warnings about shell escaping the temporary file name.
Merge branch 'rm-mbox-sync-back' into develop
view attachment fnames: history
Add user defined labels in thread view mode title
Move logic to mode status instead of buffer title
Merge pull request #239 from rakoo/add-user-labels

Add user defined labels in thread view mode title
contact-list-mode: use sup default color instead of terminal default

Addendum to https://github.com/sup-heliotrope/sup/issues/77
I found another place where sup uses the terminal default color instead
of the default text color: the contact list. With this patch, the
contact list uses colors from the colorscheme.
history: note on thread-view-mode labels
Merge #234: remove the lockfile if sup isn't already launched

Fixes #233.

Squashed commit of the following:

commit 5dd0ffec3d2aba071c02816298ad6801d690e4ae
Author: julien@macbook <julien.stechele@gmail.com>
Date:   Mon Feb 24 12:53:11 2014 +0100

    Sleep a couple of seconds before locking one more time

commit 235aff8327d8f2df8d41febbdabb481f5bd8fc9f
Author: julien@macbook <julien.stechele@gmail.com>
Date:   Mon Feb 24 12:42:04 2014 +0100

    true need a return like false

commit bf0cc9bb9e8c137be50c29a85f5ccc44b899085e
Author: julien@macbook <julien.stechele@gmail.com>
Date:   Wed Feb 19 16:21:38 2014 +0100

    false alone has no effect, use return with

commit 09f1034bc51ec6843f61f16db1ec2bd85cefc8d0
Author: julien@macbook <julien.stechele@gmail.com>
Date:   Wed Feb 19 16:20:04 2014 +0100

    Message + false

commit 58a0248486373fe26c53cc094b13ec050c982f6b
Author: julien@macbook <julien.stechele@gmail.com>
Date:   Wed Feb 19 16:15:06 2014 +0100

    Fix indentation

commit 072531a3e2d16bde21afb53b630f3c4f9031122a
Author: julien@macbook <julien.stechele@gmail.com>
Date:   Mon Feb 17 16:28:56 2014 +0100

    issue-233: remove the lockfile if sup isn't already launched
util: string, fall back to string length if Unicode.width fails
test, string length: make sure bad message line has length
util: comment on fall back
person: Don't downcase the email address

As per RFC 2821:
    The local-part of a mailbox MUST BE treated as case sensitive.
    Therefore, SMTP implementations MUST take care to preserve the case of
    mailbox local-parts. Mailbox domains are not case sensitive. In particular,
    for some hosts the user "smith" is different from the user "Smith".
Merge #256: Fix missing lines because of incorrect line width calculation
Add support for unsubscribing from URL