This patch add a new option in the handle that allows disabler to be more
aggressive when removing hidden licenses.

The default behavior is that disabler can only remove licenses that have
been checked out before the handle goes into idle status. By adding

  assume-hidden = yes

to a handle's configuration you tell disabler to remove all licenses matching
user, feature and feature version regardless of checkout time.

NB! This includes any license checked out up to the point when disabler is
doing license removal.

* Memory leak after setpwent(). Apparently the system call leaks memory. It is handled by caching
the data from this system call.

* Problems with shared memory used for signalling between parent and child processes. The shared
memory segments were not freed.