Allocation failures are not panics

[Darksonn]

This is a documentation bug report. I've noticed that functions sometimes include a section like the following:

Panics

Panics if Vec::reserve(additional) fails to reserve enough memory.

Allocation failures are handled by just calling into vec.reserve. However, the reserve method does not panic on allocation failure. Instead, it calls abort.

[joshlf]

Looks like vec.reserve bottoms out in handle_alloc_error, which may panic or abort depending on how the binary was built. Maybe this should say:

If Vec::reserve(additional) fails to reserve enough memory, extend_vec_zeroed may panic or abort depending on how the program is configured to handle allocation failure.

[joshlf]

Closed by #1478