[kernel] Avoid to create an already existing directory. Abort if a file with same path already exists.

Used by the Inout plugin, and then indirectly by Memexec.

The function given to [dynamic_register] builds directly the flag instead of
only the abstraction.

No internal representation change.

Even when no function is bound to the domain name (which should raise an error
anyway).

To also include domains enabled by option -eva-domains-function.

The logical clause and the pre-state are now optional. The function can now
be used to remove from a state all inferred properties that depend on a given
memory location.
This only impacts the cvalue domain, which is the only one to use the assign
clause.

Queries return an origin option instead of an origin.
Domains not using the origin simply return None, and no longer need to define
the origin type.