CFT: fix OfflineIMAP lockup in single-threaded mode

[Eygene Ryabinkin]

Tue, Feb 05, 2013 at 11:25:07PM +0400, Eygene Ryabinkin wrote:
> Here we go, the variant with module-global variable that holds the
> read-only copy of 'options'.  The latter is synchronized with the
> real 'options', so modifications of the real options are visible
> to the consumers of read-only instance.
> 
> Patch:
>   http://codelabs.ru/patches/offlineimap/2013-altpatch-create-global-options-instance.diff

Had reworked that one a bit: added exception throwing for modifications
and deletion of the constant object attributes.  Added testsuite for
this module.  The patch is still here,
  http://codelabs.ru/patches/offlineimap/2013-altpatch-create-global-options-instance.diff

Will commit it to the 'next' in the coming day or two if no one will
raise objections or will have ideas on how to do this in a better way.
-- 
rea