Cryptsetup is since 1.3.0 capable of setting up a loop device if the
device argument is a file.
This has the additional benefit that those loop devices will get the
AUTOCLEAR flag (available with Linux 2.6.25). This means those loop
devices will be closed as soon they're unused (on luksClose).

Especially directly after each other.

previously it had dedicated cases for listing all tombs and a singular
one, which duplicated code.
The function got reworked, that it uses a different approach for
findmnt. Instead of filtering the general result, it now uses --source
on the tomb specific crypsetup mapper. Those are searched via general
globbing of the devices in /dev/mapper. This allows to combine the
previous separate cases.
Additionally remove the usage of _sudo for findmnt, as it is not
necessary.

similar to list_tomb_mounts, rework the findmnt usage to usage of the
actual tomb mapper device.
Simplifies the awk usage and just only one argument needed for the
mapper function.

Instead of only looking for bind mounts from within a tomb due to bind-hooks, also consider bind mounts that happenfrom the outside (example: open a tomb and manually issue a mount --bind /media/tomb some/other/location).
Such a mount wouldn't be filtered before (only looking for an additional [/path/] added to TARGET.
Instead look for every mount that is related to the respective /dev/mapper/ entry of a tomb and also close or list them.
This helps to avoid to loop again against mounted tombs inside the main loop which loops over mounted tombs.

As the argument for list_tomb_mounts uses the input directly, it needs to be uniform.
Therefore one must make sure that extraneous character like parentheses are removed from the variable.
And those are in place in tombname for slam_tomb().

it may happen, that someone bind mounts manually or via an immutable setup the tomb mountdir somewhere else.
Tomb should be able to discover such mounts and close them if the tomb itself is closed.