Expect: AX    0005H
BX    ID for the new session
ES:DI addr of switcher's service-entry address
Return: AX    0000H if OK to create the session
0001H if you object to the new session
Info: Task switchers call this to let you know that a new session is
about to be created.  It gives you a chance to object to the new
session (fir instance, if you don't have enough memory to track
it safely).

When called, interrupts are enabled you may use all DOS fns.

BX will contain the session ID of the new session.  The high 4 bits
are the Switcher ID (see INT 2fH 4b03H) and the low 12 bits are
an arbitrary (not necessarily sequential) number.

ES:SI will contain the task switcher's service entry address.  Use this
address if you need to call any task-switcher service fns.

Return: AX=0000H to indicate that you don't object to the new session. If
any task returns 0001H, the session will not be started and all
tasks may receive SwNtfyFn 0006H (session has been destroyed).

INT 2fH 4bxxH (switcher functions)
- -

SwNtfy Fn 0005H: Switcher Is Creating a Session