Issue #2334689 by er.pushpinderrana, joachim: Document character limit on lock_aquire() for lock name

- Patch #1216886 by pounard: _lock_id() shouldn't use drupal_static(), any cache clear would potentially make locks stall.

#710142 by Berdir, moshe weitzman, chx: Handle exceptions in shutdown functions (with tests). Hopefully the last of these weird 'Stack frame in Unknown line 0' errors.

- Patch #251792 by pwolanin, Damien Tournoud, slantview, c960657: added a locking framework for long running operations.