Let (user space) Task ID start with 1, so 0 can be easily checked as "invalid" task ID

[fachat]

Maybe as a first iteration:

• just the mapping by adding/subtracting 1.

Then, potentially:
map 1,2,3,4,5, ... as user space task ID to the kernel space task IDs that are indexes into the task table. This would reduce potential for errors when an invalid task ID is given to the kernel.

Note: this potentially breaks API in the new GETINFO2 for example. Hopefully we can limit the effect (e.g. define TID_INVAL as GETINFO2 starting ID...)