Add OpenBSD default CA certificates file location

GitHub pull: https://github.com/OfflineIMAP/offlineimap/pull/120
Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>
Add default CA bundle location for DragonFlyBSD

Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>
Brought CustomConfig.py into more proper shape

 - Multi-line documentation for functions and methods
   now has ending triple-double-quotes on an own line,
   as per PEP 257.

 - Added documentation and comments to almost all functions
   and methods.

 - Added stub implementations for getconfig() and getsection()
   inside CustomConfig.ConfigHelperMixin to provide sane
   run-time diagnostics for classes that doesn't implement them.

Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>
Merge branch 'next'