- Replaced `session_lock` with `session_lock_manager` which is
persistent throughout the session.
- Replaced `session_lock->abandoned` with `session_lock_manager->locked`.
Old `session_lock->abandoned` is equal to
`!session_lock_manager->lock && session_lock_manager->locked`.
- Eliminated the use of global variables in `session-lock.c`.
- Changed some function names.
Currently, if the output layout changes while the session is locked,
the lock surfaces may end up wrongly positioned, which looks bad and
may reveal some of the user's workspace underneath.
To prevent this, re-align the scene trees and reconfigure the lock
surfaces when the output layout changes.
Made all header files to have LABWC_ prefix in include guard identifers.
Converted from __LABWC_ in 35 include/ files.
Converted from __LAB_ in 5 include/ files.
Added LABWC prefix to 3 include/ files.
Added include guards to 3 include/ files.
The double underscores were removed since according to C standard
those "are always reserved for any use".
